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arXiv:1505.04499v2 [astro-ph.SR] 31 May 2015
Mon. Not. R. Astron. Soc. 000, 000–000 (0000) Printed 4 June 2015 (MN L
A
T
EX style file v2.2)
Spitzer Infrared Spectrograph point source classification in
the Small Magellanic Cloud
Paul M. E. Ruffle,1,2⋆F. Kemper,2†O. C. Jones,1,3G. C. Sloan,4K. E. Kraemer,5
Paul M. Woods,6M. L. Boyer,7S. Srinivasan,2V. Antoniou,8E. Lagadec,9
M. Matsuura,10,11 I. McDonald,1J. M. Oliveira,12 B. A. Sargent,13 M. Sewi lo,14,15
R. Szczerba,16 J. Th. van Loon,12 K. Volk3and A. A. Zijlstra1
1Jodrell Bank Centre for Astrophysics, The University of Manchester, Alan Turing Building, Oxford Road, Manchester M13 9PL
2Academia Sinica, Institute of Astronomy and Astrophysics, Taipei 10617, Taiwan
3Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
4Department of Astronomy, Cornell University, Ithaca, NY 14853, USA
5Institute for Scientific Research, Boston College, 140 Commonwealth Avenue, Chestnuthill, MA 02467, USA
6Astrophysics Research Centre, School of Mathematics & Physics, Queen’s University Belfast, University Road, Belfast, BT7 1NN
7Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
8Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
9Laboratoire Lagrange, Universit´e de Nice - Sophia Antipolis, Observatoire de la Cˆote d’Azur, CNRS, 06304 Nice, France
10School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA
11Department of Physics and Astronomy, University Col lege London, Gower Street, London WC1E 6BT
12School of Physical and Geographical Sciences, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG
13Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623, USA
14Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301, USA
15Johns Hopkins University, Department of Physics and Astronomy, 366 Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218, USA
16N. Copernicus Astronomical Center, Rabianska 8, 87-100, Torun, Poland
4 June 2015
ABSTRACT
The Magellanic clouds are uniquely placed to study the stellar contribution to dust
emission. Individual stars can be resolved in these systems even in the mid-infrared,
and they are close enough to allow detection of infrared excess caused by dust. We have
searched the Spitzer Space Telescope data archive for all Infrared Spectrograph (IRS)
staring-mode observations of the Small Magellanic Cloud (SMC) and found that 209
Infrared Array Camera (IRAC) point sources within the footprint of the Surveying
the Agents of Galaxy Evolution in the Small Magellanic Cloud (SAGE-SMC) Spitzer
Legacy programme were targeted, within a total of 311 staring mode observations.
We classify these point sources using a decision tree method of object classification,
based on infrared spectral features, continuum and spectral energy distribution shape,
bolometric luminosity, cluster membership and variability information. We find 58
asymptotic giant branch (AGB) stars, 51 young stellar objects (YSOs), 4 post-AGB
objects, 22 Red Supergiants (RSGs), 27 stars (of which 23 are dusty OB stars), 24
planetary nebulae (PNe), 10 Wolf-Rayet (WR) stars, 3 H ii regions, 3 R Coronae Bore-
alis (R CrB) stars, 1 Blue Supergiant and 6 other objects, including 2 foreground AGB
stars. We use these classifications to evaluate the success of photometric classification
methods reported in the literature.
Key words: techniques: spectroscopic – surveys – galaxies: Small Magellanic Cloud
– stars: early-type, YSO, supergiants, AGB, post-AGB, planetary nebulae, late-type,
carbon, oxygen – ISM: dust, H ii regions – infrared: stars.
⋆Paul M. E. Ruffle passed away on 21 November 2013. His co- authors have finished the manuscript on his behalf, and would
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0000 RAS
2Paul M. E. Ruffle et al.
1 INTRODUCTION
The Mega-Surveying the Agents of Galaxy Evolution (Mega-
SAGE) project has obtained infrared photometric and spec-
troscopic inventories of the Magellanic Clouds with the
Spitzer Space Telescope (hereafter Spitzer ), using Spitzer
and Herschel Legacy Programmes. The initial SAGE sur-
vey (Meixner et al. 2006) detected and catalogued ∼6.9 mil-
lion point sources in the Large Magellanic Cloud (LMC)1,
while the SAGE-SMC survey (Gordon et al. 2011) detected
and catalogued ∼2.2 million point sources in the Small
Magellanic Cloud (SMC)2. Both surveys used all bands of
the Infrared Array Camera (IRAC; 3.6, 4.5, 5.8, 8.0 µm;
Fazio et al. 2004) and the Multi-Band Imaging Photometer
for Spitzer (MIPS; 24, 70, 160 µm; Rieke et al. 2004) instru-
ments on board Spitzer (Werner et al. 2004). The resolution
of the IRAC observations is ∼2′′, while for the MIPS bands,
three different resolutions apply: 6′′, 18′′ , and 40′′ for the
24, 70 and 160 µm bands respectively (Gordon et al. 2011).
To follow up on these programmes, the SAGE-Spec project
(Kemper et al. 2010) obtained 196 staring-mode pointings
using Spitzer’s Infrared Spectrograph (IRS; Houck et al.
2004, 5.2–38 µm) of positions selected from the SAGE cat-
alogue. SAGE-Spec will relate SAGE photometry to the
spectral characteristics of different types of objects in both
Magellanic Clouds, and ultimately, allow us to classify pho-
tometric point sources in both the LMC and SMC. This
characterisation of the point sources observed in the SAGE-
Spec survey, and the IRS data archive, builds an inventory
of dusty sources and their interrelation in each of the Magel-
lanic Clouds. In a first step towards this goal, Woods et al.
(2011) classified the initial 196 LMC point sources, using a
decision tree method of object classification, based on in-
frared (IR) spectral features, continuum and spectral en-
ergy distribution (SED) shape, bolometric luminosity, clus-
ter membership and variability information. The initial clas-
sification of LMC objects is being extended to ∼1,000 point
sources, covering all archival IRS observations within the
SAGE footprint (Woods et al. in prep.).
To extend the LMC classifications to the SMC, we have
searched the Spitzer data archive for IRS staring-mode ob-
servations and found 311 spectra, yielding 209 unique and
genuine point sources with IRS data within the footprint of
the SAGE-SMC Spitzer Legacy programme. The data used
in the classification process are described in Section 2. In
Section 3 we discuss the classification method, and in Sec-
tion 4 we classify the 209 SMC point sources using the deci-
sion tree method. Finally, in Section 5 we compare spectral
versus colour classifications by means of colour-magnitude
diagrams (CMDs). We use our spectroscopic classifications
to test photometric classification methods, e.g. those by
Boyer et al. (2011); Sewi lo et al. (2013) and Matsuura et al.
(2013). The classification of each of these 209 sources is part
like to dedicate it to his memory. Paul was a very enthusiastic
scientist, and a wonderful friend with a great sense of humour.
We miss him tremendously.
†Email: ciska@asiaa.sinica.edu.tw
1http://irsa.ipac.caltech.edu/data/SPITZER/docs/
spitzermission/observingprograms/legacy/sage
2http://irsa.ipac.caltech.edu/data/SPITZER/docs/
spitzermission/observingprograms/legacy/sagesmc
of the data delivery of the SAGE-Spec Legacy project to the
Spitzer Science Center and the community.3These classifi-
cations will also be used to benchmark a colour-classification
scheme that will be applied to all point sources in the SAGE
and SAGE-SMC surveys (Marengo et al. in prep).
2 DATA PREPARATION
2.1 Spitzer IRS staring mode observations
The IRS on board Spitzer covers the wavelength range 5–
38 µm. For the low-resolution mode, the spectrum splits in
two bands, short-low (SL: 5.2–14.5 µm) and long-low (LL:
14.0–38.0 µm), with almost perpendicular slits. Each seg-
ment splits into a range covered at second order (SL2, LL2),
and one at first order (SL1, LL1). The resolution varies be-
tween 60 and 130. The high resolution mode covers the wave-
length range from 10–19.6 µm (short-high; SH) and from
18.7–37.2 µm (long-high; LH) with a spectral resolution of
R∼600.
We identified 311 Spitzer IRS low- and high-resolution
staring mode observations within the footprint of the SAGE-
SMC survey (Gordon et al. 2011), not necessarily associ-
ated with a point source. We numbered these SMC IRS 1–
311, by ordering them by observing program (Project ID;
PID) first, and then the Astronomical Observation Request
(AOR) number (Table 1). Where available (for SL and LL
observations only), the reduced spectra were downloaded
from the Cornell Atlas of Spitzer IRS Sources4(CASSIS;
Lebouteiller et al. 2011), in a full resolution grid, using the
optimal extraction method. At the moment, the CASSIS
database only contains SL and LL data, but it turns out
that there are no point sources in the SMC targeted with
only SH and LH, so we will use the SL and LL data only.
The data were downloaded in the Infrared Processing and
Analysis Center (IPAC) Table format5; the file names are
also given in Table 1. As an example, the upper left panel
of Fig. 1 shows the spectrum for point source SMC IRS 110,
with the SL2 and LL2 data from CASSIS in red and the SL1
and LL1 data in blue.
The CASSIS-reduced IRS data header provides the
original PI’s requested (REQ) position and the field of view
(FOV) position, i.e. where the telescope actually pointed
(usually, but not always coincident within 1′′ of the REQ
position). In many cases, however, neither of these two po-
sitions is the same as the position at which the spectrum is
actually extracted from the slit (EXT), using the optimal
extraction method. In order to check the spectrum position
for each source, slit images were generated by over-plotting
the IRS SL and LL slit positions (recorded in each Spitzer
AOR’s BCD FITS header) on a 360′′ ×360′′ image extracted
from the SAGE-SMC 8 µm image. The REQ and EXT posi-
tions were also over-plotted on the image. In cases where the
spectrum was extracted at the FOV position (and thus an
EXT position is lacking), the FOV position was overplotted
3http://irsa.ipac.caltech.edu/data/SPITZER/docs/
spitzermission/observingprograms/legacy/sagespec
4http://cassis.astro.cornell.edu
5http://irsa.ipac.caltech.edu/applications/DDGEN/Doc/
ipac tbl.html
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0000 RAS, MNRAS 000, 000–000
Spitzer-IRS point source classification in the SMC 3
Table 1. IRS staring mode targets in the SMC. The first ten lines are presented to demonstrate the format of this table; the full table
is available on-line.
SMC IRS AOR PID PI spectrum position CASSIS file name
RA (h m s) Dec (◦ ′ ′′ )
1 3824640 18 Houck 00 46 40.32 −73 06 10.80 NULL
2 3824896 18 Houck 01 09 16.80 −73 12 03.60 NULL
3 4384000 63 Houck 01 24 07.68 −73 09 03.60 NULL
4 4384000 63 Houck 01 24 07.68 −73 09 03.60 NULL
5 4384000 63 Houck 01 24 07.68 −73 09 03.60 NULL
6 4384768 63 Houck 00 59 09.84 −72 10 51.60 NULL
7 4385024 63 Houck 00 58 52.25 −72 09 25.92 cassis tbl spcf 4385024 1.tbl
8 4385024 63 Houck 00 58 58.22 −72 09 50.76 cassis tbl spcf 4385024 2.tbl
9 4385024 63 Houck 00 58 58.80 −72 10 25.32 cassis tbl spcf 4385024 3.tbl
10 4385024 63 Houck 00 59 06.62 −72 10 25.68 cassis tbl spcf 4385024 4.tbl
Spectra for SSID: 110 AOR: 10663169 Target: MSX SMC 024
5 10 15 20 25 30 35
Wavelength (µm)
0
20
40
60
80
Fν (mJy)
90 180 270 36000 SSID: 110 PID: 3277 AOR: 10663169 Pointing: 1 Target: MSX SMC 024
0
90
180
270
360
00
00 42 52.2 −73 50 52 Requested Position
N
00 42 52.3 −73 50 51 Extracted Position
SED for SSID: 110 AOR: 10663169 Target: MSX SMC 024
0 10 20 30
Wavelength (µm)
0
20
40
60
80
100
120
140
λFλ (10−15 Wm−2)
Log SED for SSID: 110 AOR: 10663169 Target: MSX SMC 024
1 10
Wavelength (log µm)
0.1
1.0
10.0
100.0
λFλ (log 10−15 Wm−2)
Figure 1. From upper left to lower right: Example spectrum, slit image, SED and log SED plots for point source SMC IRS 110. The
spectrum plots were generated using CASSIS-reduced IRS data from the following low resolution modules: short-low 2nd order 5.2–
7.6 µm (red); short-low 1st order 7.6–14.0 µm (blue); long-low 2nd order 14.0–20.5 µm (red); long-low 1st order 20.5–37.0 µm(blue). Slit
images were created by over-plotting IRS short-low and long-low slit positions on a 360′′ ×360′′ image extracted from the SAGE-SMC
8µm image; the REQ and EXT or FOV positions were also over-plotted. SED and log SED plots (lower left and lower right panels,
respectively) were generated by combining the above IRS data with the following photometric data points: SAGE-SMC catalogue (green
diamonds): U,B,V,I(MCPS), J,H,KS(IRSF); 3.6, 4.5, 5.8, 8.0 µm (IRAC), 24 µm (MIPS); WISE catalogue (magenta triangles): J,
H,KS(2MASS), 3.4, 4.6, 12, 22 µm (WISE ).
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0000 RAS, MNRAS 000, 000–000
4Paul M. E. Ruffle et al.
instead (see upper right panel of Fig. 1 for an example for
SMC IRS 110). The slit images are useful in determining
the origin of the emission seen in the IRS spectra. The coor-
dinates in Table 1 represent, if available, the EXT position.
The next preference is the FOV position, and if neither of
these is available, the REQ position is given.
2.2 Photometric matching
In order to find matching photometry for the IRS spectra,
we searched the SAGE-SMC Single Frame + Mosaic Pho-
tometry (SMP) Archive v1.5 (Gordon et al. 2011) available
on Gator6, using, in order of preference, the EXT, FOV
or REQ spectrum positions. We searched for IRAC point
source matches within 3′′ of the spectrum positions, which
corresponds with the pointing accuracy of the IRS mode
on Spitzer. In cases where the SAGE-SMC point source
catalogue did not provide a match, we also searched the
Spitzer Survey of the Small Magellanic Cloud (S3MC) cat-
alogue7(Bolatto et al. 2007) for IRAC matches within 3′′ .
We found three sources in S3MC without a SAGE-SMC cat-
alogue counterpart. Although the S3MC data are included
in the SAGE-SMC result, both teams used different point
source extraction pipelines and the source catalogues there-
fore do not provide a one-to-one match.
Of the original list of 311 IRS staring mode observations
within the SAGE-SMC footprint, we discarded all 44 spectra
for which we could not identify an IRAC point source within
3′′ in either the SAGE-SMC or the S3MC surveys. In cases
where multiple matches were present within 3′′, we man-
ually compared the magnitudes with the flux levels of the
spectra, and used the slit images to establish which source
was responsible for the spectrum. We also consolidated du-
plicate measurements of the spectrum of a given source, as
evidenced by their SAGE-SMC or S3MC identification, into
a single entry in our analysis; this is sufficient for spectral
identification purposes. This further reduced the number by
58 to a list of 209 unique Spitzer -IRAC point sources, with
either SAGE-SMC or S3MC identifications, for which IRS
staring mode observations are available. We compiled all
relevant information in a table available online. Table 2 de-
scribes the columns of the online table. Fig. 2 shows the
distribution of the 209 sources over the SMC.
Preferring the IRAC coordinates over the spectrum co-
ordinates, we then matched the IRAC point sources to a
number of other infrared and optical photometric surveys.
We obtained MIPS-[24], [70] and [160] matches, within a
search radius of 3′′, 9′′ , and 20′′, respectively, from the
SAGE-SMC survey (Gordon et al. 2011), corresponding to
half a resolution element in these bands. We also searched
the Wide-Field Infrared Survey Explorer (WISE ) All-Sky
Source Catalog for matches within 3′′. We also searched
for AKARI matches in the N3, N4, S7, S11, L15, and S22
bands within 3′′ using the catalogue provided by Ita et al.
6Gator is the general catalogue query engine provided by the
NASA/IPAC Infrared Science Archive, which is operated by the
Jet Propulsion Laboratory, California Institute of Technology, un-
der contract with the National Aeronautics and Space Adminis-
tration.
7At the time of writing only the S3MC Young Stellar Object Cat-
alog is available in the public domain (A. Bolatto, priv. comm.).
Table 3. Classification types used in the decision tree shown in
Fig. 3, and counts for a total of 209 SMC point sources. The
last section of the table shows a breakdown of other known types
(OTHER).
Code Ob ject type Count
YSO-1 Embedded Young Stellar Objects 14
YSO-2 Young Stellar Objects 5
YSO-3 Evolved Young Stellar Objects 22
YSO-4 HAeBe Young Stellar Objects 10
HII H ii regions 3
O-EAGB Early-type O-rich AGB stars 8
O-AGB Oxygen-rich AGB stars 11
RSG Red Supergiants 22
O-PAGB Oxygen-rich post-AGB stars 1
O-PN Oxygen-rich planetary nebulae 4
C-AGB Carbon-rich AGB stars 39
C-PAGB Carbon-rich post-AGB stars 3
C-PN Carbon-rich planetary nebulae 20
STAR Stellar photospheres 4
Dusty OB stars 23
RCRB R CrB stars 3
BSG Blue Supergiant 1
WR Wolf-Rayet stars 10
OTHER B[e] stars 2
Foreground stars 2
S stars 1
symbiotic stars 1
(2010). In the near-infrared, the Two Micron All Sky Sur-
vey (2MASS) Long Exposure (6X) survey was searched
for matches within 2′′ of the IRAC positions (SAGE-SMC
matches with 2MASS), and we also used this search ra-
dius with the InfraRed Survey Facility (IRSF) catalogue
(Kato et al. 2007). The Deep Near Infrared Survey (DENIS)
of the Southern Sky catalogue (3rd release; Epchtein et al.
1999) was also searched with a 2′′ search radius. In the op-
tical, many of our sources have matches in the Magellanic
Clouds Photometric Survey (MCPS; Zaritsky et al. 2002)
and the catalogue published by Massey (2002). In both cat-
alogues we looked for matches within 1.5′′ of the IRAC po-
sition. Some of the objects in our sample are actually too
bright for those two optical surveys, and a search of the TY-
CHO catalogue with a radius of 3′′ filled in some of these
gaps. All tabulated photometry is available from the online
database (see Table 2). We only provide the magnitudes for
the purpose of evaluating the shape of the SED. Further in-
formation, including the photometric uncertainties, can be
found in the respective source tables using the designations
provided, as well as Appendix A.
2.3 Bolometric magnitudes, variability and colour
classifications
For each source bolometric magnitudes were calculated via a
simple trapezoidal integration of the SED, to which a Wien
tail was fitted to the short-wavelength data, and a Rayleigh-
Jeans tail was fitted to the long-wavelength data. The fol-
lowing SED combinations were calculated:
(i) MCPS or Massey (2002) optical photometry; JHK S
photometry; and IRAC and MIPS-[24] photometry, all as
available (mbol phot in Table 2);
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0000 RAS, MNRAS 000, 000–000
Spitzer-IRS point source classification in the SMC 5
Table 2. Numbering, names and description of the columns present in the classification table which is available on-line only.
Column Name Description
1 smc irs SMC IRS identification number of the target
2 name Name of point source targeted
3 sage spec class Source classification determined in this paper
4–5 ra spec, dec spec Position of the extracted spectrum
6 aor Spitzer Astronomical Observation Request
(AOR) number
7 pid Spitzer observing program identification number
8 pi Last name of the PI of the Spitzer PID
9 cassis file name Name of the file containing the CASSIS -reduced
Spitzer-IRS spectrum
10 irac des SAGE-SMC or S3MC IRAC point source designation matching
the extracted spectrum
11–12 ra ph, dec ph RA and Dec in degrees of the IRAC point source
13 dpos ph Distance in arcsec between the IRAC point source
and the position of the extracted spectrum
14–17 irac1, irac2, irac3, irac4 IRAC magnitudes in bands 1–4
18–20 tycho des, b tycho, v tycho TYCHO counterpart and its Band Vmagnitudes
21–25 m2002 des, u m2002, b m2002, v m2002, r m2002 Massey (2002) counterpart and its U,B,V,R
magnitudes
26–29 u mcps, b mcps, v mcps, i mcps Matching MCPS U,B,V,Imagnitudes
30–33 denis des, i denis, j denis, k denis DENIS counterpart and its I,J,KSmagnitudes
34–37 irsf des, j irsf, h irsf, k irsf IRSF counterpart and its J,H,KSmagnitudes
38–41 tmass des, j tmass, h tmass, k tmass 2MASS 6X counterpart and its J,H,KSmagnitudes
42–46 wise des, wise1, wise2, wise3, wise4 WISE counterpart and its magnitudes in the four
WISE bands
47–52 akari n3, akari n4, akari s7, akari s11, akari l15, akari l22 Matching AKARI magnitudes in bands N3, N4, S7,
S11, L15 and L22 from Ita et al. (2010)
53–54 mips24 des, mips24 SAGE-SMC MIPS-[24] designation and magnitude
55–56 mips70 des, mips70 SAGE-SMC MIPS-[70] designation and magnitude
57–58 mips160 des, mips160 SAGE-SMC MIPS-[160] designation and magnitude
59 mbol phot Mbol calculated by interpolation of JHK S, IRAC and
MIPS-[24] photometry, with a Wien and
Rayleigh-Jeans tail
60 mbol phwi as #59, but with WISE photometry added
61 mbol phsp as #59, but with the IRS spectrum added
62 mbol pwsp as #59, but with the IRS spectrum and WISE
photometry added
63–65 mbol mcd, lum mcd, teff mcd Mbol calculated using the SED fitting code from
McDonald et al. (2009, 2012); only good fits are included
66–67 id groen, per groen Source ID and variability period in days from
Groenewegen et al. (2009)
68–72 ogle3id, ogle3mean i, ogle3mean v, ogle3amp i, ogle3period Source ID and variability information from the
OGLE survey
73 boyer class Colour classification from Boyer et al. (2011)
74 matsuura class Colour classification from Matsuura et al. (2013)
75 sewilo class Colour classification from Sewi lo et al. (2013)
(ii) like (i) but combined with the WISE photometry
(mbol phwi);
(iii) like (i) but combined with the IRS spectrum
(mbol phsp);
(iv) like (i) but combined with both the WISE photome-
try and the IRS spectrum (mbol pwsp);
For sources where there is little reprocessing of the
optical emission, i.e. little infrared excess, bolometric
magnitudes were calculated using an SED fitting code
(McDonald et al. 2009, 2012). This code performs a χ2-
minimisation between the observed SED (corrected for inter-
stellar reddening) and a grid of bt-settl stellar atmosphere
models (Allard et al. 2011), which are scaled in flux to derive
a bolometric luminosity. This SED fitter only works effec-
tively where a Rayleigh-Jeans tail is a good description of
the 3 to 8 µm region, and provides a better fit to the opti-
cal and near-IR photometry than a Planck function. For the
most enshrouded stars, fitting the SED with ‘naked’ stellar
photosphere models leads to an underestimation of the tem-
perature and luminosity, due to circumstellar reddening, and
hence the integration method (above) for calculating Mbol
is preferred for very dusty sources. Experience shows that
good fits can be separated from bad fits in the NIR: if the
model and observations differ at I,J,Hor KSby more than
a magnitude in any band, the fit is considered bad. This
retains the cases where the difference between model and
observations in the MIR or FIR is large, but often in these
cases the excess emission is unrelated to the point sources.
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0000 RAS, MNRAS 000, 000–000
6Paul M. E. Ruffle et al.
Figure 2. The SMC IRS targets distributed on the sky, overlaid upon a SAGE-SMC IRAC 8 µm map. The colour of the points represent
our classifications, according to the legend. All four YSO subcategories and the H ii regions are grouped together in red. The class “stars”
contains objects classified as STAR and the sub-category of dusty OB stars. The “O-rich evolved” category contains O-EAGB, O-AGB,
O-PAGB and O-PN objects, and likewise the “C-rich evolved” category groups together C-AGB, C-PAGB and C-PN objects. The Red
Supergiants are a group by themselves, and “other” contains all other categories (see Table 3).
In cases where it is related to the point source, making the
source very red, the values calculated by trapezoidal inte-
gration provide a better estimate of Mbol .Teff ,Mbol and L
for the good fits are included in the online table as teff mcd,
mbol mcd and lum mcd, respectively (see Table 2).
The sample was then matched to the Optical Gravita-
tional Lensing Experiment (OGLE-III) catalogue of long-
period variables in the SMC (Soszy´nski et al. 2011) and
Groenewegen et al. (2009) to obtain variability periods, and
the variability information is included in the on-line table
(see Table 2).
Finally, we included a number of colour classification
schemes for comparison. First, Boyer et al. (2011) have ex-
tended the classification scheme developed by Cioni et al.
(2006) to classify dusty mass-losing evolved stars into
subcategories, using IRAC, MIPS and NIR colours. We
checked our source list against their catalogue for matches.
Their classifications (O-AGB, C-AGB, x-AGB, aO-AGB,
RSG, RGB and FIR) are included in the on-line table as
boyer class (see Table 2). Definitions of these classes can be
found in Boyer et al. (2011). Furthermore, we also applied
the colour classification scheme proposed by Matsuura et al.
(2013) to the sources in our list. This classification scheme
is also designed to distinguish between various kind of very
red objects, to estimate the dust production rate. We ap-
plied the cuts described by Matsuura et al. (2013, Fig. 4, 5)
on our sample and list the classifications that follow from
these cuts (O-AGB, C-AGB, RSG) in our online table, as
matsuura class (see Table 2). The last colour classification
scheme we apply is the one proposed by Sewi lo et al. (2013)
for YSOs, who applied classification cuts in the five different
infrared CMDs, followed by visual inspection of images and
SED fitting to select YSO candidates from the SAGE-SMC
survey. We checked our source list against their catalogue
and identified ‘high-reliability’ and ‘probable’ YSO candi-
dates accordingly (sewilo class; Table 2).
3 THE CLASSIFICATION METHOD
To classify our sample of 209 SMC point sources for which
IRS staring mode data exist, we follow the method described
by Woods et al. (2011). Fig. 3 shows a restyled version of
the classification decision tree. We made enhancements to
the tree, which will be discussed in this section.
A literature search was performed for each object to
retrieve other information useful in the process of classifica-
tion, including (but not limited to) determination of stellar
type, luminosity, age of nascent cluster of stars (if the ob-
ject was found to be a member of a cluster), H αdetections,
etc. This information was used in addition to the spectro-
scopic data, the photometric matches and derived bolomet-
ric luminosity, and the variability data, described in Sec. 2,
to classify the sources. Any existing classification from the
literature was used as a starting point before our spectral
classification. Appendix A provides a brief summary of the
literature survey for each object.
As in Woods et al. (2011), we adopt the following
categories for our point source classification. Low- and
intermediate-mass (M < 8 M⊙) post-main-sequence stars
are classified by chemistry (O- or C-rich) and by evolution-
ary stage (asymptotic giant branch, post-asymptotic giant
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0000 RAS, MNRAS 000, 000–000
Spitzer-IRS point source classification in the SMC 7
YES
NO
START
YES
NO
NO
YES
YES
NO
NO
YES
YES
YES
NO
YES
NO
YES
NO
NO
NO
YES
YES
NO
NO
YES
NO
NO
YES
YES
NO
YES
NO
YES YES
NO
YES NO
NO
YES
YES
NO
NO
YES
YES
NO
NO
NO
YES YES
Redshifted
features?
Featureless
continuum with
PAHs or atomic
emission lines?
Galaxy
Atomic
emission
lines?
Evolved
YSO-3
Spectrum
rises
>30 μm?
HII
region
Strong PAH features?
3.3 6.2 7.7 8.6
11.2 12.7 16.4 μm C-PN
O-PN
Solely
molecular
features?
Ice
absorption
at 15 μm?
C-rich features?
5.0 7.5 13.7 μm
absorption
C-AGB
Mbol <–7.1 and
SED peak ~1 μm?
O-AGB
RSG
Dust
features? SED peaks
longward
of 2 μm?
RCrB
Star
O-rich features?
10, 20 μm silicate
emis. or absorp.
C-rich features?
5.0 7.5 13.7 μm abs.
11.3 21 30 μm emis.
Other
21 μm feat. or strong
11.3 & 30 μm feats. or
double-peaked SED?
C-PAGB
C-PN
C-AGB
Atomic
emission lines?
Falling spectrum over
range 20–32 μm?Distinctly
double-peaked
SED?
O-PAGB
Atomic
emission
lines?
High
excitation
lines? [NeV]
[NeVI] [OIV]
HII
region
O-PN
Member of
young cluster?
RSG
Mbol <–7.1
and SED
peak ~1 μm?
O-AGB
Ice
absorption
at 15 μm?
Silicate
absorp-
tion?
Strong
10 μm
emission?
Other HAeBe
YSO-4 YSO-2 Embedded
YSO-1
Embedded
YSO-1
Figure 3. The logical steps of the classification decision tree, where Spitzer IRS spectra (λ= 5.2–38 µm), associated optical, NIR,
WISE, IRAC and MIPS photometry, luminosity, variability, age and other information are used to classify SMC infrared point sources.
See Table 3 for key to classification group codes. Figure restyled in appearance from the one published by Woods et al. (2011).
c
0000 RAS, MNRAS 000, 000–000
8Paul M. E. Ruffle et al.
branch and planetary nebula), hence our groupings O-AGB,
O-PAGB, OPN, C-AGB, C-PAGB, C-PN. We propose
an enhancement of the classification tree by Woods et al.
(2011) to include early-type O-rich AGB stars, namely O-
EAGB. These stars do not show any evidence for dust fea-
tures in their infrared spectra, but they do show long pe-
riod variability in OGLE and MACHO and some evidence
for continuum infrared excess. Although these stars are in
the early stages of AGB evolution, they are most likely more
evolved than genuine early-AGB (E-AGB) stars, which have
not yet started helium shell burning. E-AGB stars do not
normally show long period variability. We assume that O-
EAGB stars are thermally-pulsing AGB-type objects prior
to the onset of, or just beginning, significant dust forma-
tion. More massive and luminous red supergiants have a
class of their own, RSG. Young stellar objects can be clas-
sified phenomenologically into four groups, YSO-1, YSO-2,
YSO-3, YSO-4 (see Woods et al. 2011 for the definition of
these classes). Stars showing a stellar photosphere, but no
additional dust or gas features, or long-period variability,
are classified as STAR. One observational program focussed
on stars showing a far-infrared excess in their MIPS pho-
tometry (Sheets et al. 2013; Adams et al. 2013), due to the
illumination and heating of interstellar dust (the Pleiades ef-
fect); these objects are classified as a subcategory of STAR:
dusty OB stars. The tree also distinguishes galaxies (GAL;
even though none are actually found in the present work)
and H ii regions (HII), and we furthermore have a class for
R CrB stars (labeled RCRB in the classification table). Fi-
nally the classification OTHER exists for ob jects of known
type which do not belong in the categories above and do not
follow from the classification tree (e.g. B[e] stars). The na-
ture of these objects are usually identified by other means,
and as such reported in the astronomical literature.
3.1 Classification Process
Each source was classified independently by at least three of
the co-authors. In cases where the classification was unan-
imous, it was simply adopted as the final classification,
whereas in those cases where some discrepancies occurred,
we asked additional co-authors to classify the sources, to set-
tle the issue. In some cases, a discussion on the nature of the
source ensued. We aimed to reach consensus among the co-
authors on the nature of a source in cases where differences
in classification occurred.
The lead author of this work (Paul Ruffle) developed an
internal web browser-based classification tool, to facilitate
the classification process. The decision tree was built into
the tool as a series of questions, and the collected data were
available in tabulated form. For each source the classification
tool provided a slit image and plots of its spectrum, SED, log
SED and bolometric magnitudes (see Fig. 1 for examples).
Each author was free to use either the decision tree logic or
their own method of classification. There was also room for
the co-authors to add additional comments to the table.8
8Although we were able to use this tool to its conclusion and
generate the final classification table prior to Paul Ruffle’s unex-
pected death, the tool was intended to be available online indefin-
tely, for application on other data collections. Unfortunately, the
4 SAGE-SPEC POINT SOURCE
CLASSIFICATION
Table 3 lists the classification types, used in the decision tree
shown in Fig. 3, and counts for a total of 209 SMC point
sources, for which Spitzer-IRS staring mode observations are
available. The classifications are also shown overplotted on
the map of the SMC (Fig. 2).
Fig. 4 shows typical spectra of objects classified as one
of the four YSO type objects, as well as a typical IRS spec-
trum of an H ii region. The numbering 1–4 for the YSO
classes represent an evolutionary sequence, with YSO-1 be-
ing the most embedded and YSO-4 the most evolved type of
YSO, namely Herbig Ae Be (HAeBe) stars. This is evident
from the spectral appearance of the silicate feature, which
appears in absorption towards YSO-1 objects, then gradu-
ally in self-absorption (YSO-2), until it finally appears in
emission (YSO-3, YSO-4), for less embedded objects. The
spectra of the YSO-1 objects also show ice absorption fea-
tures, for instance the CO2ice feature at 15.2 µm, further
evidence of their early evolutionary phase. Polycyclic aro-
matic hydrocarbons (PAHs) are seen in the spectra of the
YSO-3, YSO-4 and H ii classes, indicative of a UV radiation
field. Atomic lines are also seen, particularly in YSO-3 and
Hii objects, and the latter category shows a rising contin-
uum indicative of cold dust in the vicinity of the ionizing
star.
Fig. 6 shows typical spectra in the group of oxygen-
rich evolved stars. The earliest type of O-rich AGB stars
are shown at the bottom of the plot (O-EAGB), and the
spectra shown here do not show any dust features, while the
signature of oxygen-rich molecular species may be present in
the spectra. A slight change of slope due to a small infrared
excess caused by thermal dust emission, may be visible in
the SED, however. Later type O-AGB stars, red supergiants
(RSG) and oxygen-rich post-AGB stars (O-PAGB), share
spectroscopic characteristics, such as the presence of silicate
emission features, although the detailed shape can be differ-
ent. To distinguish between the RSG and O-AGB category, a
bolometric luminosity cut of Mbol =−7.1 is used, while the
distinction between O-AGB and O-PAGB is based on the
presence of a detached shell where a double-peaked SED is
used as a criterion for the latter category. This is demon-
strated in the lower right panel of Fig. 5 showing the SED
of the sole O-PAGB object in the sample, LHA 115-S 38
(SMC IRS 257). O-rich PNe (O-PN) may still show a dis-
tinguishable oxygen-rich chemistry in their dust mineralogy
(although not in the case shown), but they are discriminated
from C-PN using the presence of PAH lines in the spectra
of the carbon-rich objects.
Fig. 7 gives an overview of the 5–38 µm spectral appear-
ance of carbon-rich evolved stars. Tracers of the carbon-rich
chemistry are the C2H2molecular absorption bands at 5.0,
7.5 and 13.7 µm, the SiC dust feature at 11.3 µm, the 21-
µm feature (which remains unidentified and really peaks at
20.1 µm), and the so-called 30-µm feature, which has re-
cently been suggested to be due to the same carbonaceous
internet service provider where this website was hosted recently
stopped providing this service and as of yet, the co-authors have
not been able to reconstruct and resurrect the website with the
classification tool.
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0000 RAS, MNRAS 000, 000–000
Spitzer-IRS point source classification in the SMC 9
Figure 4. Example spectra in the YSO and H ii categories. From
bottom to top, we show examples of YSO-1 through 4, and a spec-
trum of an H ii region, in an evolutionary sequence from young to
more evolved. The spectra are labelled with their SMC IRS num-
ber. Discernible spectral features are indicated with tick marks
and labels at the top of the diagram. The heavily embedded YSO-
1 spectrum shows silicates and ices in absorption. The YSO-2
spectrum shows silicate in self-absorption. Silicate emission and
PAH features are visible in the spectrum of the YSO-3, YSO-4
and H ii objects, albeit i n different ratios. The H ii region has a
rising SED slope.
compound that carries the continuum (Otsuka et al. 2014),
while the MgS identification is under debate (Zhang et al.
2009; Lombaert et al. 2012). Again, the distinction between
the C-PAGB and C-AGB categories is based on whether
the SED is double-peaked, which is evidence for a detached
shell, indicating mass loss has stopped. Fig. 5 shows two
clear examples of this, namely SMC IRS 243 and SMC
IRS 268. SMC IRS 95 is confirmed to be a C-PAGB star
(Kraemer et al. 2006; van Loon et al. 2008), despite its ab-
sence of a double-peaked SED. C-PAGB and C-PN also show
the UV-excited PAH features, and in case of the C-PN, the
presence of atomic emission lines.
Fig. 8 shows typical spectra of a number of star-like cat-
egories, namely (from top to bottom) stellar photospheres,
with no discernible dust features in the spectrum; R CrB
stars, which only appear to show a dust continuum with
no spectral substructure; a Blue Supergiant in our sample,
which appears to have a strong far-infrared excess on top
of a stellar photosphere, and finally Wolf-Rayet stars, which
may form dust and show the corresponding infrared excess
10-5
10-4
10-3
10-2
10-1
1 10
10-5
10-4
10-3
10-2
10-1
1 10
λFλ (10-12 W m-2)
λ (µm)
SMC IRS 95 SMC IRS 243
SMC IRS 268 SMC IRS 257
Figure 5. SEDs of the four post-AGB stars in the sample. The
SMC IRS spectra 95, 243 and 268 correspond to C-PAGB ob-
jects, while SMC IRS 257 is the spectrum of a O-PAGB ob-
ject. The black lines represent the IRS spectra, while the red
diamonds correspond to the collected photometric measurements
for each source. The double-peaked structure used as a distin-
guishing feature is visible in the SEDs of 243, 268 and 257.
2MASS J00364631−7331351 (SMC IRS 95) does not show a dou-
ble peaked structure, but its C-PAGB nature is confirmed using
near-infrared spectroscopy and the PAH features in the IRS spec-
tra (See Appendix A).
in the spectrum. The Blue Supergiant and the Wolf-Rayet
star classifications are taken from the literature, and are not
based on the infrared spectroscopy. Similarly, Fig. 9 shows
the spectra of the object types group under OTHER, of
which the classifications are taken from the literature (see
Appendix A). The examples shown in Fig. 9 represent from
top to bottom a B[e] star, a foreground AGB star, an S star
and a symbiotic star. Their infrared spectra are not used to
achieve this classification, and the IRS data are plotted only
for illustration.
Figs. 10–12 show the 209 classified point sources on the
[8.0] versus J−[8.0] CMD and two different colour-colour di-
agrams (CCDs), overlayed on the SAGE-SMC point source
catalogue (Gordon et al. 2011) in gray scale.
The [8.0] versus J−[8.0] CMD (Fig. 10) shows a large
spread for the population of 209 ob jects. The stellar atmo-
spheres (STAR) and Wolf-Rayet stars have colours more or
less indistinguishable from the bulk of the SAGE-SMC cat-
alogue (with J−[8.0] ∼0–1 mag), and modest brightness at
8.0 µm, even though these stars are amongst the brightest
stars in the optical in the SMC. All other categories dis-
played are bright in the IRAC [8.0] band, and often show
considerable redness in their J−[8.0] colour. In this dia-
gram RSG, O-AGB/O-EAGB, C-AGB and YSOs (all classes
combined), are reasonably well separated from each other,
although there are some interlopers. It appears to be difficult
to separate PNe and YSOs on the one hand, and the most
extreme C-AGB stars and YSOs on the other hand. Distin-
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0000 RAS, MNRAS 000, 000–000
10 Paul M. E. Ruffle et al.
Figure 6. Example spectra of different types of O-rich evolved
stars. The spectra are labelled with their SMC IRS number. At
the top the wavelengths of the silicate features and spectral lines
are labelled. At the bottom of the plot the spectrum of the E-
OAGB star closely resembles a stellar photosphere. The spectra of
the O-AGB, RSG and O-PAGB star all show the silicate emission
features. Distinguishing between these three types is not possible
from IRS spectroscopy alone, and additional information on SED
shape and bolometric luminosity is required. The top spectrum
is characeteristic of a O-PN.
guishing between the four YSO classes is also not possible
in this diagram.
Fig. 11 is a CCD composed of the four IRAC bands,
namely the [3.6]−[4.5] versus [5.8]−[8.0] colours. The advan-
tage of using a CCD is that it is distance independent. The
coverage of the sample of 209 objects fans out nicely over
colour-colour space. In this diagram, the stars and WR stars
no longer separate well from the rest of the sample, however
it now appears easier to separate YSOs from C-AGB stars on
the one hand and PNe on the other hand. However, C-PAGB
and O-PAGB stars probably overlap with the colour-colour
space taken up by YSOs, as they transition from the AGB
region to the PN region in the diagram. But as this phase
is short-lived, pollution of the colour-selected YSO sample
with post-AGB stars is limited. Subdivision within the YSO
category is still not possible, and also the O-(E)AGB objects
do not seem to occupy a unique part of colour-colour space.
Finally, Fig. 12 shows the J−KSversus [8.0]−[24] CCD.
In this CCD, the C-AGB objects are easily separated from
all other types of objects, as their J−KScolour quickly in-
creases, with increasing [8.0]−[24]. For O-(E)AGB stars and
Figure 7. Example spectra of C-rich evolved stars. From bottom
to top two C-AGB stars are shown, followed by a C-PAGB and a
C-PN. All four spectra are labelled with their SMC IRS number.
The tick marks at the top show the position of characteristic
spectral features. In the C-AGB spectra the molecular absorption
bands of C2H2are visible, as well as emission due to SiC and
possibly MgS (30µm, not in all sources). The C-PAGB object
no longer shows the molecular absoprtion bands, but the SiC
and the MgS (not always) are still visible. Other features include
PAH bands and the 21-µm feature. The infrared spectrum of C-
PN objects shows the spectral features due to PAHs and atomic
lines.
RSGs this increase is less steep, forming a separate branch in
the middle of the plot. O-PN and C-PN group together with
YSOs towards the top of the diagram, showing the highest
values of [8.0]−[24], against modest J−KSreddening.
5 COMPARISON WITH EXISTING COLOUR
CLASSIFICATIONS
These 209 spectral classifications will allow us to verify ex-
isting infrared photometric classification schemes that have
come out of recent studies of the Magellanic Clouds. We
compare our results with three distinct colour classifica-
tion schemes: a) the JHK Scolour classification scheme
for evolved stars by Cioni et al. (2006), expanded by
Boyer et al. (2011) to include mid-IR wavelengths; b) the
IRAC classification scheme for AGB stars and RSGs by
Matsuura et al. (2013), which is based on the previous
work by Matsuura et al. (2009) on the LMC; and c) the
Spitzer classification scheme to select YSO candidates by
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0000 RAS, MNRAS 000, 000–000
Spitzer-IRS point source classification in the SMC 11
Figure 10. [8.0] vs J−[8.0] CMD. The gray scale in the background represents a density plot of the SAGE-SMC point source catalogue,
while the coloured symbols are the sources classified in this work. For clarity, the plot is duplicated with the coloured symbols spread
out over the left- and right-hand plot according to the legend.
Figure 11. [5.8]−[8.0] vs [3.6]−[4.5] all-IRAC CCD. Description as in Fig. 10.
Sewi lo et al. (2013), based on earlier work by Whitney et al.
(2008).
5.1 Boyer et al. (2011)
In order to classify all evolved stars in the SAGE-SMC
(Gordon et al. 2011) data, Boyer et al. (2011) devised a clas-
sification scheme, based on the 2MASS classification scheme
presented by Cioni et al. (2006). The basis for this classifica-
tion scheme is the Kversus J−KSCMD (Fig. 13), showing
the cuts for the RSG, O-AGB and C-AGB object classes, su-
perposed on the SAGE-SMC point sources (grey pixels). The
dotted line refers to the tip of the Red Giant Branch (RGB),
and Boyer et al. (2011) use this line to separate RGB stars
from the AGB and RSG categories. Photometrically classi-
fied objects from Boyer et al. (2011) are shown as coloured
pixels. At the red end of the diagram, some photometrically
classified C-AGB stars appear below the diagonal cut, or
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0000 RAS, MNRAS 000, 000–000
12 Paul M. E. Ruffle et al.
Figure 12. [8.0]−[24] vs J−KSCCD. Description as in Fig. 10.
even below the dotted line corresponding to the tip of the
RGB. These objects are called extreme AGB stars, predom-
inantly carbon-rich, which are defined as J−[3.6] >3.1
mag (e.g., Blum et al. 2006). Often these objects are so red,
that they are not detected in 2MASS JHK S, and alterna-
tive selection criteria in the mid-infrared are required. The
reader is referred to Boyer et al. (2011) for a detailed de-
scription. The larger symbols in Fig. 13 represent the sample
of Spitzer-IRS spectroscopically classified ob jects described
in this work.
5.1.1 C-AGB stars
Objects showing the C-AGB spectral signature are
all classified as either C-AGB or x-AGB (most of
which are expected to be C-rich), according to the
Boyer et al. (2011) classification, although three of these
objects are not included in the catalogue published by
Boyer et al. (2011). These objects (OGLE SMC-LPV-
7488 (SMC IRS 44; SSTISAGEMA J004903.78−730520.1);
2MASS J01060330−7222322 (SMC IRS 109; SSTISAGEMA
J010603.27−722232.1); and 2MASS J00561639−7216413
(SMC IRS 129; SSTISAGEMA J005616.36−721641.3)) are
among a larger set of objects that had not been properly
matched between the IRAC Epochs in the mosaicked cata-
logue (Srinivasan et al. in prep.). These objects were thus
missing photometric measurements in the point source cata-
logue, in some bands, and were therefore not classified (cor-
rectly) by Boyer et al. (2011). The on-line table described
by Table 2 shows the correct photometry for these three
targets.
5.1.2 Red Supergiants
Most of the 21 spectroscopically classified RSGs indeed fall
within the RSG strip defined by Boyer et al. (2011). Only
three of the objects classified as an RSG by us were clas-
sified differently by Boyer et al. (2011) using only the pho-
tometry: HV 11417 (SMC IRS 115) is designated as a FIR
object by Boyer et al. (2011); Massey SMC 55188 (SMC IRS
232) as an O-AGB star; and IRAS F00483−7347 (SMC IRS
98) as an x-AGB star. HV 11417 is a variable star with
a period of 1092 days, and an amplitude in the I band of
1.9 mag (Soszy´nski et al. 2011). Due to this large ampli-
tude, the timing of the observations affects the IR colours
of the object significantly, which is why the photometry
measurements show a small positive slope between 8 and
24 µm ([8.0] −[24] >2.39 mag), causing it to be classified
as a FIR object by Boyer et al. (2011), while the slope of
the IRS spectrum is distinctly negative. If we disregard the
FIR colour cut, which is meant to separate AGB stars from
objects such as YSOs, PNe and background galaxies, this
object would have been classified as an O-AGB star, which
deviates from our determination of RSG, and from past clas-
sifications (Elias et al. 1980). The bolometric luminosity of
this object is close to the RSG/O-AGB boundary, and could
be affected by the variability of the object too. The large am-
plitude favours a classification as luminous AGB star over
a RSG. RSGs were separated from O-AGB stars using the
classical AGB bolometric magnitude limit (Fig. 3), but this
boundary is not absolute. AGB stars undergoing hot bottom
burning can be brighter than this limit, while less-evolved
RSGs can be fainter. This causes some disagreement in clas-
sifications of stars near the boundary.
Alternatively, the luminosity boundary between RSG
and O-AGB may not be properly represented by the cuts in
the KSvs J−KSdiagram from Boyer et al. (2011). Similary,
the misclassification of Massey SMC 55188 also suggests that
the bolometric cut we applied to distinguish between O-
AGB stars and RSGs does not correspond to the boundaries
between these two categories in the KSvs J−KSCMD.
IRAS F00483−7347 clearly shows an oxygen-rich chemistry
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0000 RAS, MNRAS 000, 000–000
Spitzer-IRS point source classification in the SMC 13
Figure 13. The Boyer et al. (2011) photometric classification, based on the work by Cioni et al. (2006), applied to the SMC. Boyer et al.
(2011) begin with the J−KSclassification shown here, then use 3.6 and 8-µm photometry to recover and classify the dustiest sources.
The slanted lines in this KSvs J−KSCMD represent the boundaries of the C-AGB, O-AGB and RSG categories, and the horizontal
dotted line shows the boundary between the tip of the RGB and the earlier type AGB stars. In gray scale the SAGE-SMC point source
catalogue is shown in the form of a density plot. The lilac, yellow and dark pink dots represent the RSG, O-AGB and C-AGB objects,
as they are classified in the KSvs J−KSCMD. The light pink dots are the x-AGB stars, selected by Boyer et al. (2011), replacing any
KSvs J−KSclassification. The x-AGB objects fall mostly within the C-AGB boundaries. The coloured symbols represent the objects
spectrally classified in this work, following the legends and spread out over two panels for clarity.
in its spectrum, with the presence of the amorphous silicate
bands at 9.7 and 18 µm. The object is heavily embedded,
with a very red SED, and the 9.7-µm feature starts to show
signs of self-absorption. IRAS F00483−7347 demonstrates
that not all x-AGB objects are in fact carbon-rich AGB
stars.
5.1.3 O-AGB stars
All objects classified as O-EAGB in this work are similarly
classified as O-AGB by Boyer et al. (2011). The spectrally-
confirmed O-AGB objects, however, show a much wider
spread in colour-magnitude space than the defined strip, and
they encroach on the photometrically-defined RSG, C-AGB
and FIR categories. In particular, only two spectroscopi-
cally classified O-AGB stars, HV 12149 (SMC IRS 45) and
2MASS J00444463−7314076 (SMC IRS 259) are classified as
O-AGB based on photometry. One object (HV 1375; SMC
IRS 110) is classified as a C-AGB based on its photomet-
ric colours, and a further six ob jects (RAW 631, 2MASS
J00463159−7328464, 2MASS J00445256−7318258, BMB-B
75, IRAS F01066−7332 and HV 12956) are apparently suf-
ficiently red ([8.0] −[24] >2.39 mag) to be classified as
FIR, even though they are not background galaxies, YSOs
or PNe. These six objects are heavily embedded, and show
the effect of a high optical depth in the relative strength of
the 18 µm silicate band with respect to the 9.7-µm band.
They also show evidence for the presence of crystalline sili-
cates in their spectrum, another sign of high optical depth
(Kemper et al. 2001; Jones et al. 2012). Finally, HV 2232
(SMC IRS 230) and HV 11464 (SMC IRS 309) are photo-
metrically classified as Red Supergiants (Boyer et al. 2011)
(see the table described by Table 2).
5.1.4 Additional sources
The further nine interlopers in the C-AGB/x-AGB section
of the CMD defined by Boyer et al. (2011) are a mixed
bag of objects, all but one falling in the x-AGB category.
These objects reflect selection biases and include rare cat-
egories of previously known types such as R CrB stars
(2MASS J00461632−7411135, 2MASS J00571814−7242352
and OGLE SMC-SC10 107856), an S star (BFM 1) and a
B[e] star (Lin 250). These object types are not included
in the Boyer et al. (2011) classification scheme, and could
therefore never have agreed with the spectral classification.
True misclassifications are the objects thought to be C-rich
AGB stars, only to be revealed to be something else based
on their IRS spectroscopy. These include O-PAGB star
LHA 115-S 38, YSO-2 object 2MASS J01050732−7159427,
and RSG IRAS F00483−7347. NGC 346:KWBBe 200 is
a special case, as it was thought to be a B[e] supergiant
(Wisniewski et al. 2007a), but its classification has recently
been revised to a YSO (Whelan et al. 2013), in line with our
classification of YSO-3 (See Appendix A).
The FIR category defined by Boyer et al. (2011) was
introduced to exclude YSO s, compact H ii regions, PNe and
background galaxies from the AGB/RSG sample, by apply-
ing the [8] −[24] >2.39 mag cut, corresponding to a rising
continuum. Indeed, 14 out of 23 FIR objects are either C-PN
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0000 RAS, MNRAS 000, 000–000
14 Paul M. E. Ruffle et al.
Figure 8. Example spectra of ob jects with stellar photospheres
or similar. Shown here from bottom to top are the spectra of a
WR star, a BSG, a R CrB star and a regular stellar photosphere,
labelled with their SMC IRS number. The WR star shows some
atomic lines in its spectrum (marked at the top of the diagram),
but the other spectra are rather featureless. The infrared excess
in the R CrB and BSG objects are caused by dust emission.
(three objects) or YSOs (11 objects), according to their IRS
spectra. The remaining nine FIR objects include the six O-
AGB stars discussed in Sec. 5.1.3, but also a symbiotic star
(SSTISAGEMA J005419.21−722909.7; SMC IRS 260) and a
C-PAGB (2MASS J00364631−7331351; SMC IRS 95), both
of which are classified based on their IRS spectra.
5.2 Matsuura et al. (2013)
The second classification scheme was proposed by
Matsuura et al. (2009) to identify mass-losing O-rich and
C-rich AGB stars, as well as Red Supergiants, in order to
estimate the dust production budget in the LMC, separated
out by C-rich and O-rich chemistries. The scheme is based
on the IRAC bands, using the [8.0] vs [3.6]−[8.0] CMD, and
separates out the O-rich AGB stars and RSGs on the one
hand, and C-rich AGB stars on the other hand (Fig. 14).
Matsuura et al. (2009) used only this diagram to classify
the IRAC point sources in the LMC, but for the SMC,
Matsuura et al. (2013) added an extra step to overcome pol-
lution between the categories for redder [3.6]−[8.0] sources.
Indeed, from Fig. 14 it is clear that the red part of the C-
AGB section is dominated by sources identified as YSOs (tan
diamonds), while a significant fraction of the O-AGB objects
Figure 9. Example IRS spectra of objects in the OTHER cat-
egory. From bottom to top we show the spectra of a symbiotic
star, an S star, a foreground (Galactic) O-AGB star and a B[e]
star, all labelled with their SMC IRS number. Relevant spectral
features due to silicates are labelled at the top of the figure.
(blue diamonds) also fall within the C-AGB section. In the
second step, MIPS and NIR data are included, and a com-
plex series of cuts is made in the KS–[24] vs KS–[8.0] CCD
(see Fig. 5 in Matsuura et al. 2013, ; the equations are not
provided). In cases where the classification using the KS–
[24] vs KS–[8.0] diagram (Fig. 15) deviates from the [8.0]
vs [3.6]−[8.0] classification, the KS–[24] vs KS–[8.0] classi-
fication takes preference. Most spectral classifications agree
with the photometric classification in the second step (see
Fig. 15). In case where sources were only classified in one of
the two steps, we used that classification. We have executed
this classification method for our 209 sources, and included
the results in the table described by Table 2.
5.2.1 Carbon-rich AGB stars
The two-step classification described by Matsuura et al.
(2013) correctly identifies most of the spectroscopically
classified C-AGB stars in our sample as such. In only
three cases was an object photometrically classified as
being oxygen-rich (RSG/O-AGB), while the spectroscopy
shows the carbon-rich nature of the source. These sources
are 2MASS J00515018−7250496 (SMC IRS 103); 2MASS
J00524017−7247276 (SMC IRS 127) and IRAS 00350−7436
(SMC IRS 238). IRAS 00350−7436 is among the brightest
mid-infrared objects in the SMC, and falls above the C-AGB
c
0000 RAS, MNRAS 000, 000–000
Spitzer-IRS point source classification in the SMC 15
Figure 14. First step of the Matsuura et al. (2013) photometric classification method, based on the work by Matsuura et al. (2009),
applied to the SMC. The solid lines in this [8.0] vs [3.6]-[8.0] CMD represent the boundaries of the C-AGB category, and provide a lower
boundary to the RSG/O-AGB category. The dashed line shows the position of the YSO limit used by Boyer et al. (2011). All colours
have the same meaning as in Fig. 13.
Figure 15. Second step of the Matsuura et al. (2013) photometric classification method. The solid lines in this KS–[24] vs KS–[8.0]
CCD represent the boundaries of the various evolved star categories. All colours have the same meaning as in Fig. 13.
cut in Fig. 4 of Matsuura et al. (2013), due to its exceptional
brightness.
Furthermore, the classification of several C-AGB stars
by Matsuura et al. (2013) disagrees with the spectral clas-
sification. These include: a C-rich post-AGB star (2MASS
J00364631−7331351; SMC IRS 95), four O-rich early-type
AGB stars (HV 1366, HV 11303, HV 838 and HV 12122;
SMC IRS 36, 38, 39 and 116, respectively), a WR star
(HD 5980; SMC IRS 281), a RSG (HV 11262; SMC IRS
111), a YSO-3 object (NGC 346:KWBBe 200; SMC IRS
19), the three R CrB stars (2MASS J00461632−7411135,
2MASS J00571814−7242352 and OGLE SMC-SC10 107856;
SMC IRS 94, 114 and 245, respectively), the two fore-
ground O-rich AGB stars NGC 362 SAW V16 and HV 206,
c
0000 RAS, MNRAS 000, 000–000
16 Paul M. E. Ruffle et al.
the S star BFM 1 and the symbiotic star SSTISAGEMA
J005419.21−722909.7. The last four objects are all in the
OTHER category, which contains subclasses the work by
Matsuura et al. (2013) does not seek to classify. The four
O-rich early-type objects have actually long been recognized
as such, in some cases their nature was already known in the
1980s, and they fall only slightly outside the boundaries in
Fig. 5 of Matsuura et al. (2013). The RSG HV 11262 has
very similar KS–[8.0] and KS–[24] colours to the four O-
EAGB objects. 2MASS J00364631−7331351 is not properly
filtered out by Fig. 5, as it falls just below the KS–[24] =
8 mag cutoff that is meant to exclude YSO, C-PN, and C-
PAGB objects from the C-AGB category. The R CrB stars
represent a rare class which, not surprisingly, overlaps in in-
frared colours with the C-AGB stars, as it is believed that
the dust in these stars is carbonaceous (Feast 1986). HD
5980 is the only WR star that is classified by Matsuura et al.
(2013). Although other WR stars do appear in Fig. 14, they
do not receive a classification as they are too faint in the [8.0]
band. HD 5980 is considerably brighter in the [8.0], and is
the only WR star with a MIPS-[24] detection in the SMC
(Bonanos et al. 2010). Closer inspection of the IRS spectrum
seems to suggest that a chance superposition with a compact
Hii region gives rise to this 24 µm detection, and is actually
not a detection of the WR star itself. Thus, the position of
HD 5980 in Fig. 15 and the classification following from it,
should be disregarded. Finally, NGC 346:KWBBe 200 is a
curious object, which, from its IRS spectrum appears to be a
YSO, but has characteristics in common with B[e] stars (See
Appendix A). It falls well outside the box defined for YSO,
C-PN and C-PAGB, perhaps due to its unusual nature.
5.2.2 Oxygen-rich AGB stars and RSGs
Since the main purpose of the classification scheme by
Matsuura et al. (2013) is to determine the dust production
by evolved stars distinguished by carbon-rich and oxygen-
rich chemistry, the subdivision in types of evolved stars
within the oxygen-rich class is less important. In fact, in the
first step, all types of oxygen-rich evolved stars (AGB stars
and RSGs) are lumped together as RSG/O-AGB (Fig. 14),
while in the second step a subdivision is made between
O-AGB (which also includes RSG) and O-AGB/O-PAGB
(Fig. 15). The latter category contains the more evolved
O-AGB stars. Thus, a total of three partially overlapping
categories exist. The RSG/O-AGB category contains ob-
jects that are classified as such in the first step, but re-
mained unclassified in the second step. This class contains
only three objects (2MASS J00515018−7250496, 2MASS
J00524017−7247276 and IRAS 00350−7436), which are all
C-AGB according to their IRS spectroscopy, and are already
discussed in Sec. 5.2.1.
The 24 objects classified as O-AGB in the second step
are indeed all O-AGB or RSG objects according to their IRS
spectroscopy. However, the category O-PAGB/O-AGB con-
tains a more diverse range of objects. Of the eight SMC IRS
objects classified by the method of Matsuura et al. (2013)
to be in this category only four are genuine O-rich evolved
stars: IRAS F00483−7347 (SMC IRS 98) is a RSG according
to our classification, LHA 115-S 38 (SMC IRS 257) is found
to be a O-PAGB ob ject, and 2MASS J00463159−7328464
(SMC IRS 121) and HV 12956 (SMC IRS 277) are O-AGB
stars. The other objects in this category include two carbon-
rich evolved stars, 2MASS J00444111−7321361 (SMC IRS
268), a C-PAGB object, and Lin 343 (SMC IRS 161), a C-
PN. Both of these objects should have fallen in the YSO/C-
PN/C-PAGB, but with KS–[24] just below 8 mag they both
just miss the cutoff. Since Fig. 15 does not show any O-
rich ob jects in the vicinity of the K–[24] = 8 mag cutoff
between C-rich and O-rich post-AGB objects, a case can be
made to lower the cutoff slightly. Finally, the remaining two
misclassified objects in the O-PAGB/O-AGB category by
Matsuura et al. (2013) are spectrally classified as B[e] stars
in the OTHER category. They are RMC 50 (SMC IRS 193)
and Lin 250 (SMC IRS 262).
When checking the reverse direction, we find that all
objects classified by us as O-AGB are indeed identified as
either O-AGB or as O-PAGB/O-AGB according to the clas-
sification scheme by Matsuura et al. (2013). However, this
classification scheme misclassifies all objects identified as O-
EAGB by us. According to the scheme by Matsuura et al.
(2013), they are either C-AGB (See Sect. 5.2.1; four out of
eight objects), or remain unclassified, as they have [3.6] −
[8.0] <0.7 mag, rendering them unclassifiable in Fig. 14, and
have KS−[8.0] <0.5 mag and KS−[24] <0.5 mag, which
causes them to fall outside all boundaries in Fig. 15. This
also happens to six of the 22 ob jects classified by us to be
RSGs; one is misclassified as a C-AGB (See Sect. 5.2.1), and
the other five do not receive a classification because their
colours are too blue (i.e. their mass-loss rates are too low).
Our sample of 209 targets with IRS spectra contains
only one oxygen-rich post-AGB star, which agrees with
the O-PAGB/O-AGB classification from Matsuura et al.
(2013).
5.3 Sewi lo et al. (2013)
The third classification scheme that we compare with is the
method developed by Whitney et al. (2008) and refined by
Sewi lo et al. (2013) to select YSO candidates. From the set
of CMDs used by Whitney et al. (2008), Sewi lo et al. (2013)
selected a combination of five different CMDs to select YSO
candidates in the SMC. Two of these diagrams are repro-
duced in this work, with the 209 IRS point sources overplot-
ted (Figs. 16 and 17). After the initial colour selection of
YSO candidates, Sewi lo et al. (2013) performed additional
tests, including a visual inspection of the imaging, a check
against the SIMBAD and other catalogues for known non-
YSO sources, and fitting against the YSO SED grid calcu-
lated by Robitaille et al. (2006). Sewi lo et al. (2013) arrive
at a list of approximately 1000 ‘high-reliability’ and ‘proba-
ble’ YSOs in the SMC.
Although Figs. 16 and 17 appear to show considerable
amount of pollution from non-YSO IRS staring mode tar-
gets, as well as many confirmed YSOs based on the IRS
data straying out of the defined boxes, it is the combina-
tion of the five CMDs, along with the additional non-colour
based checks that yields a highly reliable YSO candidate list.
Indeed, the Sewi lo et al. (2013) classification favours relia-
bility over completeness, and CMD areas with significant
pollution due to other sources (background galaxies, PNe)
have been excluded. The list of 209 IRS staring mode point
sources contains nine objects classified as probable YSOs by
Sewi lo et al. (2013), and 45 high-reliability YSO candidates.
c
0000 RAS, MNRAS 000, 000–000
Spitzer-IRS point source classification in the SMC 17
Figure 16. One of the CMD diagrams used in the Sewi lo et al. (2013) selection method for candidate YSOs, based on the work by
Whitney et al. (2008). This [8.0] vs [4.5]-[8.0] CMD diagram shows the cut used in solid black lines. In gray scale the SAGE-SMC point
source catalogue is shown in the form of a density plot. The light blue dots represent the YSO candidates finally selected by Sewi lo et al.
(2013). The coloured symbols show the location of the objects spectrally classified in this work, spread out over two panels for clarity.
(Sewi lo et al. 2013), based on (Whitney et al. 2008)
Figure 17. As Fig. 16, but now for [8.0] vs [8.0]-[24].
Of the high-reliability YSOs for which IRS observations are
available, we find that the vast majority are indeed YSOs
(covering all four classes). Only two objects turn out to
be something different: H i i region IRAS 00436−7321 (SMC
IRS 310) and C-PAGB object 2MASS J01054645−7147053
(SMC IRS 243). Among the probable YSO candidates, the
success rate is lower: four out of nine are not YSOs, upon
inspection of their IRS spectra. RMC 50 (SMC IRS 193) is
a B[e] star, while SMP SMC 11 (SMC IRS 32), LHA 115-N
43 (SMC IRS 155) and Lin 49 (SMC IRS 292) are actually
C-PN objects.
Furthermore, there are three YSO-3 type objects, as
spectrally classified, that are not identified as YSO candi-
dates by Sewi lo et al. (2013). These are NGC 346:KWBBe
c
0000 RAS, MNRAS 000, 000–000
18 Paul M. E. Ruffle et al.
200 (SMC IRS 19), 2MASS J00465185−7315248 (SMC IRS
269) and LHA 115-N 8 (SMC IRS 274).
6 SUMMARY
We have analysed all 311 Spitzer-IRS staring mode obser-
vations within the SAGE-SMC IRAC and MIPS coverage
of the SMC (Gordon et al. 2011). After removing IRS ob-
servations of extended emission, blank sky and duplicate
observations, we find that 209 unique IRAC point sources
were targeted. We applied the infrared spectroscopic clas-
sification method devised by Woods et al. (2011), with the
addition of one more category, namely O-EAGB stars (early-
type oxygen-rich AGB stars). We find that the Spitzer-IRS
staring mode sample of point sources in the SMC contains
51 YSOs, subdivided in 14 embedded YSOs (YSO-1), 5 less-
embedded YSOs (YSO-2), 22 evolved YSOs (YSO-3) and 10
HAeBe type objects (YSO-4). Furthermore, we find the sam-
ple contains 46 oxygen-rich evolved stars: 8 O-EAGB stars,
11 O-AGB stars, 22 RSGs, 1 O-PAGB object and 4 O-PN
objects. 62 objects turn out to be carbon-rich evolved stars,
namely 39 C-AGB stars, 3 C-PAGB objects and 20 C-PN
objects. The sample also includes 3 R CrB stars, 1 BSG
and 10 WR stars. 27 objects show stellar photospheres, 23
of which were selected based on their MIPS-[24] excess, and
labelled by us as dusty OB stars. It turns out that the 24-
µm emission is in general not related to the host OB star
(Adams et al. 2013; Sheets et al. 2013). Finally, the sample
includes a small number of other objects (OTHER), which
do not follow from the classification method. These include
2 B[e] stars, 2 foreground oxygen-rich AGB stars, an S star,
and a symbiotic star.
In this work, we have compared the resulting spectral
classifications with the outcome of photometric classifica-
tion schemes. It should be noted that the spectroscopic ob-
servations are obtained in 14 different observing programs,
with a diverse range of science goals. Thus, there is no ho-
mogeneous coverage of colour-magnitude space, and it will
be impossible to quantify the goodness of any given pho-
tometric classification method. Furthermore, the observing
programs tend to target rare types of sources in a dispro-
portionate amount, and some of these rare type of sources
(R CrB stars, WR stars, B[e] stars, etc.) are not included
in photometric classification schemes, precisely because they
are rare. Thus, these objects tend to pollute the classifica-
tion schemes discussed here, but statistically they are rather
insignificant.
We reviewed three different photometric classification
schemes for infrared sources in the SMC: the schemes by
Boyer et al. (2011) and Matsuura et al. (2013) for evolved
stars, and the classification scheme to select candidate YSOs
by Sewi lo et al. (2013). The latter scheme is not a pure
photometric classification, as it includes additional steps,
such as visual inspection of the direct environment of the
point source in imaging, checks against existing catalogues
and fitting against the grid of YSO SEDs calculated by
Robitaille et al. (2006). However, as discussed in Sec. 5.3,
the 54 overlapping sources from this work with the result-
ing YSO candidate list are mostly correctly classified. Only
a few sources are misclassified in either direction, i.e. three
spectroscopically confirmed YSOs were not on the candidate
list by Sewi lo et al. (2013), and six sources on the candidate
list were found to be something else upon inspection of their
IRS spectroscopy. All-in-all we conclude that the YSO can-
didate list produced by Sewi lo et al. (2013) is reliable, with
48/54 sources indeed being YSOs and the high-reliability
sources doing better than the probable sources. Only three
spectroscopically confirmed YSOs were missed due to un-
usual infrared colors.
The two photometric classification methods for evolved
stars can be directly compared to each other. The method
by Boyer et al. (2011) has its focus on identifying the en-
tire dusty evolved star population, while the Matsuura et al.
(2013) method is mainly driven by the motivation to de-
termine the carbon-rich and oxygen-rich dust production
rates. Thus, in the later method, correct identification of
lower mass-loss rate stars is not so important. Both meth-
ods can be used to estimate the integrated dust production
rate. Due to the low metallicity of the SMC, carbon-rich
evolved stars are more numerous (Blanco et al. 1978, 1980;
Lagadec et al. 2007), and the carbon stars have, on average,
the highest mass-loss rates. Thus, identifying carbon stars
correctly is important as they dominate the dust budget
(Matsuura et al. 2009; Boyer et al. 2012; Riebel et al. 2012).
Apart from rare object classes, Boyer et al. (2011) very ef-
ficiently separate C-AGB stars from the other classes, only
classifying one non-C-AGB star as C-AGB star, while classi-
fying all genuine C-AGB objects as C-AGB. Matsuura et al.
(2013) do slightly worse, with three genuine C-AGB objects
being classified as something else, and a number of objects,
including some rare types, incorrectly classified as C-AGB
star.
On the oxygen-rich side, we find that Matsuura et al.
(2013) perform better for the high-mass loss rate objects (O-
AGB stars), but that they perform rather poorly on the low-
mass rate objects (O-EAGB stars), while the performance
of the Boyer et al. (2011) classification method is reversed
because of overlap between high-mass AGB stars and RSGs
near the classical AGB limit.
Finally, we note that of the two steps involved in
the classification method by Matsuura et al. (2013), the
second step (Fig. 15) matches very well with the ac-
tual spectroscopic classification. It has been introduced by
Matsuura et al. (2013) as a correction on the first step from
Matsuura et al. (2009), but almost all photometric classi-
fications currently included in the online table described
by Table 2 correspond to the second step, and most of
the time match the spectroscopic classification, rendering
the first step practically unnecessary. Thus, in case of the
Matsuura et al. (2013) classification scheme, applying only
the second step, as demonstrated in Fig. 15, would suffice
for dusty sources.
ACKNOWLEDGEMENTS
The authors wish to thank Paul Ruffle’s partner Rose
Wheeler. Rose provided access to Paul’s notes and files,
which allowed us to finish this work. PMER thanks
Academia Sinica Institute of Astronomy and Astrophysics
(ASIAA) for their financial support and hospitality during
the preparation of this work. The authors thank David Whe-
lan for making available Spitzer spectra of point sources
c
0000 RAS, MNRAS 000, 000–000
Spitzer-IRS point source classification in the SMC 19
described in his 2013 paper. Astrophysics at JBCA is sup-
ported by STFC. F.K. acknowledges support from the for-
mer National Science Council and the Ministry of Science
and Technology in the form of grants NSC100-2112-M-
001-023-MY3 and MOST103-2112-M-001-033-. B.A.S. ac-
knowledges support from NASA ADP NNX11AB06G.
R.Sz. acknowledges support from the Polish NCN grant
2011/01/B/ST9/02031. The research presented here was
conducted within the scope of the HECOLS International
Associated Laboratory, supported in part by the Polish NCN
grant DEC-2013/08/M/ST9/00664 (E.L.; R.Sz). This work
is based (in part) on observations made with the Spitzer
Space Telescope, obtained from the NASA/IPAC Infrared
Science Archive, both of which are operated by the Jet
Propulsion Laboratory, California Institute of Technology
under a contract with the National Aeronautics and Space
Administration. This publication makes use of data prod-
ucts from the Wide-field Infrared Survey Explorer, which is
a joint project of the University of California, Los Angeles,
and the Jet Propulsion Laboratory/California Institute of
Technology, funded by the National Aeronautics and Space
Administration. Some of the data presented in this paper
were obtained from the Mikulski Archive for Space Tele-
scopes (MAST). STScI is operated by the Association of
Universities for Research in Astronomy, Inc., under NASA
contract NAS5-26555. Support for MAST for non-HST data
is provided by the NASA Office of Space Science via grant
NNX13AC07G and by other grants and contracts. This re-
search has also made use of the SAGE CASJobs database,
which is made possible by the Sloan Digital Sky Survey Col-
laboration; SAOImage DS9, developed by Smithsonian As-
trophysical Observatory; the VizieR catalogue access tool,
CDS, Strasbourg, France; the SIMBAD database, operated
at CDS, Strasbourg, France; and NASA’s Astrophysics Data
System Bibliographic Services.
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APPENDIX A: LITERATURE-BASED
CLASSIFICATION SUPPORT FOR SAGE-SPEC
OBJECTS
NGC 346 MPG 320 (SMC IRS 16) derives its name from
the catalogue by Massey et al. (1989). Simon et al. (2007)
list it as entry no. 79, a probable YSO, consistent with
our classification as a YSO-2. However, Lebouteiller et al.
(2008) suggest that this point source is not stellar but rather
a Photon-Dominated Region (PDR). Whelan et al. (2013),
who list this as PS12, follow that suggestion. Furthermore,
Kamath et al. (2014) list it as a PN candidate. This source is
also known to be an infrared variable (Polsdofer et al. 2015).
NGC 346 MPG 454 (SMC IRS 18) derives its name from
the catalogue by Massey et al. (1989). It is located at the
position of N66, an H i i region (Henize 1956). This source
also occurs in the list of candidate PNe by Kamath et al.
(2014). Chandra X-ray observations reveal that NGC 346
MPG 454 is one of the brightest blue stars in the NGC 346
cluster (Naz´e et al. 2002). Indeed, the infrared part of the
spectrum is dominated by a massive YSO (Sabbi et al. 2007;
Whelan et al. 2013), in the latter work catalogued as PS9.
NGC 346:KWBBe 200 (SMC IRS 19) is also known as NGC
346 MPG 466 (Massey et al. 1989). It is known to show
Hαemission (Meyssonnier & Azzopardi 1993). It occurs in
the list of PN candidates by Kamath et al. (2014). The
source was recognized as a classical Be star by Keller et al.
(1999), and it also derives its name from this catalogue.
Wisniewski et al. (2007b) performed a study of classical Be
stars in NGC 346, and in a detailed follow-up paper on NGC
346:KWBBe 200 alone they concluded that this object is
in fact a dusty B[e] supergiant (Wisniewski et al. 2007a).
However, recently Whelan et al. (2013) suggested that NGC
346:KWBBe 200 is not an B[e] supergiant, but rather a Her-
big AeBe star, based on the presence of silicate emission
features, PAHs and cold dust. In this paper, we classify this
object as an YSO-3.
NGC 346 MPG 534 (SMC IRS 20) derives its name from
the catalogue by Massey et al. (1989). The location coin-
cides with that of the N66A H ii region (Henize 1956), but
also with two class I protostars, of which the heaviest is
thought to b e 16.6 M⊙(Simon et al. 2007), later updated
to 17.8 M⊙(Whelan et al. 2013). Heydari-Malayeri & Selier
(2010) report that an O8 star is responsible for ionizing the
N66A H ii region. This source is a known infrared variable
(Polsdofer et al. 2015, Riebel et al. in prep.).
NGC 346 MPG 605 (SMC IRS 21) was identified for the
first time as an H αemitter (N66B; Henize 1956), and then in
the survey of NGC 346 by Massey et al. (1989) (star number
605) and classified as a red star. Kamath et al. (2014) list
this object as a PN candidate. The star (also known as NGC
346:KWBBe 448) has been then observed by Keller et al.
(1999) and classified as having Be spectral type. The spectral
type has been established also by Martayan et al. (2010) as
being B0:. The star (95) has also been observed with F555W
(V) and F814W (I) Hubble Space Telescope ACS filters by
Gouliermis et al. (2006) (see also Hennekemper et al. 2008).
The star seems to be located close to the border between
upper main sequence (UMS) and red giant branch (RGB).
Similar observations have been performed by Sabbi et al.
(2007) (source 17) and the obtained magnitudes may sug-
gest that the star is a red giant branch (RGB) source. In
the infrared this source has been detected by ISO -CAM
(source F - Contursi et al. 2000) and then by Spitzer (see
Bolatto et al. 2007). Using SED fits Simon et al. (2007) clas-
sify the source as Class I YSO. The SL Spitzer spectrum
has been analyzed by Whelan et al. (2013) (source PS6),
and shows silicate emission features, which is rare among
young star clusters. The reduced spectrum presented by
Whelan et al. (2013) does not show H2S(3) emission at 9.67
µm, while it seems to be present in our reduced spectrum.
Whelan et al. (2013) assume that the optical star related to
this IR source has spectral type O5.5V (star number 37 in
Hennekemper et al. 2008). However this star is located more
than 3 arcsec (about 1 pc) from the IR source, and probably
unrelated.
NGC 346 MPG 641 (SMC IRS 22). The optical counterpart,
located at about 0.8 arcsec from the extracted position, was
detected for the first time by Massey et al. (1989). Better
photometry has been obtained by Heydari-Malayeri & Selier
(2010) using the NTT (star N66A-2). The star has been
classified as an UMS star (Gouliermis et al. 2006). Near-
infrared observations with the VLT have been performed
by Gouliermis et al. (2010, ID number 1043), who con-
clude that this is a classical Be star with approximately
B0.5 V spectral type. In the infrared this source has been
detected by ISO-CAM (source H - Contursi et al. 2000),
Spitzer (Bolatto et al. 2007), and Herschel (Meixner et al.
2013). The SL Spitzer spectrum has been analyzed by
Whelan et al. (2013) (source PS4). It shows that at this
position the extended emission is significant and ‘optimal
extraction’ is required. Using SED fits Simon et al. (2007)
classify the source as a Class I YSO, while we conclude that
this is an H i i region.
LHA 115-N 1 (SMC IRS 26) has been detected as an H α
emission-line object by Henize (Henize 1956), and classi-
fied by Lindsay (1961) as a probable planetary nebula.
Its nature as a planetary nebula has been confirmed by
Sanduleak et al. (1978, SMP SMC 1). Bernard-Salas et al.
(2009) already presented the IRS spectrum, showing that
this object has an extremely strong 11.3-µm feature due to
SiC emission. Further discussion of this object is given by
Otsuka et al. (2013).
LHA 115-N 4 (SMC IRS 27) is also catalogued as Lin 16,
and SMP SMC 3. It is a well known SMC planetary nebula
first catalogued by Henize (1956) as an emission line ob-
ject. It was subsequently identified as a planetary nebula in
Lindsay (1961). It was noted as a lower excitation object
in Morgan (1984). Various optical spectroscopic observa-
tions were carried out in the late 1980s and early 1990s, but
the first determination of the C/O ratio was carried out by
c
0000 RAS, MNRAS 000, 000–000
24 Paul M. E. Ruffle et al.
Vassiliadis et al. (1996) showing that the nebula is carbon-
rich. There were no mid-infrared observations of this object
prior to the Spitzer spectroscopy which was presented in
Bernard-Salas et al. (2009). Their classification of the spec-
trum as being carbon-rich agrees with ours.
LHA 115-N 6 (SMC IRS 28) is another well-studied plan-
etary nebula in the SMC: it is also known as SMP SMC 6,
Lin 33, IRAS 00395−7403, LI-SMC 12, GSC 09141−007041,
and 2MASS J00412777−7347063. The object was first noted
as an emission-line object by Henize (1956) and classified
as a planetary nebula by Lindsay (1961). The object is
bright enough to have been detected by the Infrared As-
tronomical Satellite (IRAS), and aside from the original
IRAS PSC there are pointed observations for this object
(Schwering & Israel 1989). The star was found to be of Wolf-
Rayet type by E. J. Wampler (unpublished, 1978: reported
by Monk et al. 1988). The nebula was initially found to be
oxygen-rich by Vassiliadis et al. (1996); however this was re-
vised to carbon-rich by Stanghellini et al. (2009) wherein the
carbon abundance is determined from HST observations and
combined with a previous ground-based oxygen abundance.
The latter result is consistent with our spectral classifica-
tion of C-PN, which is the same as the classification from
Bernard-Salas et al. (2009) where the Spitzer spectrum was
first published.
LHA 115-N 67 (SMC IRS 29) was discovered by Henize
(1956) and identified as a planetary nebula by Lindsay
(1961). The object has many other names including Lin 333,
SMP SMC 22, and DENIS-P J005837.0−7131548. It also
appears to be a super-soft X-ray source detected by Ein-
stein,ROSAT, and XMM (i.e. Pellegrini & Fabbiano 1994;
Sturm et al. 2013). Our classification of the object as an O-
rich PN based on the infrared spectrum is consistent with
the abundance determinations of Leisy & Dennefeld (1996)
which suggests C/O of 0.275 from combined optical and IUE
spectroscopy. Similar abundance results were obtained by
Vassiliadis et al. (1998).
Lin 536 (SMC IRS 30) is a PN with cold dust compared
to other Magellanic Cloud PNe (SED peaks around 30 µm
Bernard-Salas et al. 2009). HST ACS prism spectra show it
is somewhat carbon-poor, with an A(C)∼7, while other
PNe in the SMC have A(C)>8 (Smith et al. 1995).
LHA 115-N 70 (SMC IRS 31) was discovered by Henize
(1956), and identified as a planetary nebula by Lindsay
(1961) under the name Lin 347. It is also known as
2MASS J00591608−7201598 and SMP SMC 24. No car-
bon abundance was available for this nebula before the
measurement of Stanghellini et al. (2009) which, along
with a previous oxygen abundance determination from
Leisy & Dennefeld (1996), suggests that the object has
C/O just larger than unity. The mid-infrared spectrum of
the object was considered as being unusual (but carbon-
rich) in Bernard-Salas et al. (2009), and some of the
emission features were identified as due to fullerenes by
Garc´ıa-Hern´andez et al. (2011). These are all consistent
with our classification as a C-PN.
SMP SMC 11 (SMC IRS 32). is a well known PN. Other
names for this object include LHA 115-N 29, Lin 115, and
IRAS 00467−7314. The object was first discovered by Henize
(1956) as an emission-line object, and it was classified as a
planetary nebulae by Lindsay (1961). The carbon-rich na-
ture of the nebula was confirmed from HST observations
well before there was any mid-infrared spectroscopic infor-
mation available (i.e. Stanghellini et al. 2003b). Due to the
relatively strong mid-infrared emission the object was de-
tected by IRAS in the PSC and was the subject of pointed
observations as reported by Schwering & Israel (1989).
HV 1366 (SMC IRS 36). This O-EAGB object has long been
known to be an oxygen-rich AGB star (Catchpole & Feast
1981), with a period of 293 days (Wood et al. 1983); it is also
known to vary in the infrared (Polsdofer et al. 2015, Riebel
et al. in prep.). Repeated searches do not show detectable
enhanced Lithium abundances due to hot bottom burning
in 4-8 M⊙AGB stars (Smith & Lambert 1990; Smith et al.
1995). Sloan et al. (2008) rep ort a revised perio d of 305 days
based on MACHO data, and classify the Spitzer IRS spec-
trum as 1.N. The corresponding blackbody temperature was
found to be (2270 ±560) K. OGLE variability data also ex-
ist (Soszy´nski et al. 2011). Boyer et al. (2012) estimate that
HV 1366 has a dust mass loss rate of 10−10.1M⊙yr−1.
HV 11303 (SMC IRS 38). This object is recognized as a
variable oxygen-rich AGB star with a period of 534 days
by Wood et al. (1983), in agreement with our classifica-
tion of O-EAGB. The star shows enhanced Lithium abun-
dances due to hot bottom convective envelope burning
(Smith & Lambert 1990; Smith et al. 1995). The red spectra
are dominated by CN bands, showing signs of enhancements
in 13CN (Brett 1991), which is further evidence for hot bot-
tom burning processes. Sloan et al. (2008) assign a spectral
classification of 1.N, and fit a blackbody of 2130 ±240 K to
the SED.
HV 838 (SMC IRS 39). This object was initially thought
to be a Red Supergiant, showing strong hydrogen emis-
sion (Lloyd Evans 1971; Humphreys 1979), but later rec-
ognized to be an oxygen-rich AGB star (Wood et al. 1983).
Yang & Jiang (2012) consider HV 838 as an RSG candi-
date, but notice that it is indeed an outlier with respect
to the RSG population. A period of 654 days was rep orted
by Lloyd Evans (1985), which was later revised to 629 days
based on the MACHO data (Cioni et al. 2003), however
Sloan et al. (2008) report a period of 622 days, based on
the MACHO data. Riebel et al. (in prep.) also find it to
vary in the infrared. HV 838 shows Li i6707-˚
A absorption,
a consequence of hot bottom convective envelope (HBCE)
burning (Smith et al. 1995). The IRS spectrum is classified
as 1.N by Sloan et al. (2008), with a blackbody temperature
of 2320 ±320 K. Garc´ıa-Hern´andez et al. (2009) detect Zr
and derive its abundance, and report an upper limit for the
Rb abundance.
HV 11366 (SMC IRS 41). This is an oxygen-rich AGB
star with a period of 366 days (Catchpole & Feast 1981;
Wood et al. 1983), in agreement with our classification of O-
EAGB. Its sp ectrum shows strong Li iabsorption features at
6707 ˚
A, indicative of hot bottom burning (Smith & Lambert
1989, 1990; Plez et al. 1993; Smith et al. 1995). TiO bands
are also visible in the red spectra, but there is no clear sign
of CN, and the C/O ratio is estimated to be 0.4-0.8 (Brett
1991). This member of NGC 292 has an effective tempera-
ture of 3450 K, with log g= 0.00 cm s−2and a metallicity of
[Fe/H] = −0.42 (Soubiran et al. 2010). Sloan et al. (2008)
classify the Spitzer IRS spectrum as 1.N:O::, with a black-
body temperature of 2230 ±300 K. OGLE (Soszy´nski et al.
2011) and MACHO (Yang & Jiang 2012) variability data
are available.
c
0000 RAS, MNRAS 000, 000–000
Spitzer-IRS point source classification in the SMC 25
OGLE SMC-LPV-7488 (SMC IRS 44) is a Mira variable
with a period of 434 days, and an amplitude of 1.54 mag-
nitude, derived from its OGLE ligthcurve (Soszy´nski et al.
2011). It is also variable in the infrared (Polsdofer et al.
2015, Riebel et al. in prep.). It is known to be an carbon-
rich object from the optical spectrum (Lloyd Evans 1980),
consistent with our classification of C-AGB.
HV 12149 (SMC IRS 45). In agreement with our re-
sult, this object was recognized as an O-rich AGB
star (Wood et al. 1983), with a period of 742 days
(Payne-Gaposchkin & Gaposchkin 1966). This star is also
an infrared variable (Polsdofer et al. 2015, Riebel et al. in
prep.). Enhanced Li iabsorption indicative of hot bot-
tom burning is not detected (Smith & Lambert 1990;
Smith et al. 1995), however, very strong TiO bands are
visible in the red spectrum (Brett 1991), pointing to a
low C/O ratio. VO bands are also present (Brett 1991).
A search for OH maser emission only yielded an upper
limit of 0.04 Jy at 1612 MHz (Wood et al. 1992). Sloan et al.
(2008) classify the Spitzer IRS spectrum as 2.SE8, and
the dust mass loss rate has been estimated to be 10−9.0
M⊙yr−1(Boyer et al. 2012). OGLE (Soszy´nski et al. 2011)
and MACHO (Yang & Jiang 2012) variability data are avail-
able.
HV 11223 (SMC IRS 46) is known to be a semi-regular
variable from its OGLE lightcurve, and is also known as
OGLE SMC-LPV-1141 (Soszy´nski et al. 2011). Smith et al.
(1995) show that it is in fact an O-rich AGB star with Li i
6707-˚
A detection, with logǫ(Li) = 3.5.
Dachs SMC 2-37 (SMC IRS 47). This object, also known
as Massey SMC 59803, is known to be an M supergiant
(Humphreys 1979), in agreement with our classification. Its
spectral type is reported to be M0-1 I (Massey & Olsen
2003), although Levesque et al. (2006) believe it to be K2-3
I. Modelling of optical spectra results in determinations of
Teff = 4100 K, AV= 0.93, log g= 0.0 (model) or −0.2 (ac-
tual) and R= 900 R⊙(Levesque et al. 2006). The Spitzer
IRS spectrum is classified as 2.SE4u (Sloan et al. 2008),
looking similar to the ISO -SWS spectra of RSGs in the
h and χPerseus supergiant cluster (Sylvester et al. 1998),
and a C class PAH spectrum (Peeters et al. 2002). The pe-
riod is derived from MACHO data and found to be 547 ±
17 days, with a long secondary period of 2543 ±38 days
(Yang & Jiang 2012). This source is also variable in the in-
frared (Polsdofer et al. 2015).
SMC-WR9 (SMC IRS 57) is a WN3ha Wolf-Rayet star
with a possible spectroscopic binary orbit of 37.6 days
(Morgan et al. 1991; Massey & Duffy 2001; Foellmi et al.
2003). The star is modelled to be 94,000–168,000 L⊙and
to have a wind velocity of 1616 km s−1and a mass-loss rate
˙
Mof 1.4–3.5 ×10−6M⊙yr−1(Nugis et al. 2007).
SMC-WR10 (SMC IRS 58), also known as 2MASS
J00452890−7304458, is a single WN3ha Wolf-Rayet star, ly-
ing in nebulous knot e12 within NGC 249 (Massey & Duffy
2001; Foellmi et al. 2003; Crowther & Hadfield 2006). The
star is modelled to be 120,000–240,000 L⊙and to have
a wind velocity of 1731 km s−1and ˙
M= 2 −5×
10−6M⊙yr−1(Nugis et al. 2007). Its spectrum is noted for
having strong nebulosity (Massey & Duffy 2001).
SMC-WR12 (SMC IRS 60), also known as Massey SMC
54730 (Massey 2002), was identified as a WN3–4.5 Wolf-
Rayet star by Massey et al. (2003).
GSC 09141-05631(SMC IRS 61), also known as SMC-WR1,
is a Wolf-Rayet star of spectral type WN3ha (Bonanos et al.
2010).
SMC-WR2 (SMC IRS 64) is a single WN5ha Wolf–Rayet
star with surrounding nebulosity (Azzopardi & Breysacher
1980; Massey & Duffy 2001; Foellmi et al. 2003). The star
has an estimated luminosity of 320,000 L⊙and ˙
M= 7 −8×
10−6M⊙yr−1(Martins et al. 2009).
SMC-WR3 (SMC IRS 66) is a binary (WN3h+O9:)
Wolf–Rayet star with a spectroscopic period of 10 days
(Azzopardi & Breysacher 1980; Massey & Duffy 2001;
Foellmi et al. 2003). It is thought to be a lower-mass,
evolved, H-rich object evolved from a 40–50-M⊙star
(Marchenko et al. 2004). This star appears to be interacting
with the surrounding ISM, producing a kidney-shaped
nebulosity (Gvaramadze et al. 2011).
SMC-WR4 (SMC IRS 68) is a binary WN6h+ Wolf–
Rayet star with a photometric period of 6.55 days
(Azzopardi & Breysacher 1980; Massey & Duffy 2001;
Foellmi et al. 2003). The system has an estimated luminos-
ity of 800,000 L⊙and a combined effective temperature of
∼42 500 K (Martins et al. 2009).
RMC 31 (SMC IRS 70), also known as SMC-WR6,
is a 6.5-day binary (WN4:+O6.5I:) Wolf–Rayet star
showing X-ray emission and long-period variability
(Azzopardi & Breysacher 1980; Massey & Duffy 2001;
Foellmi et al. 2003).
SMC-WR11 (SMC IRS 85), also known as 2MASS
J00520738−7235385, is a single WN4h:a Wolf–Rayet
star with appreciable reddening (Massey & Duffy 2001;
Foellmi et al. 2003). The star is modelled to be 210,000–
390,000 L⊙and have a wind velocity of 1616 km s−1and
˙
M= 2 −5×10−6M⊙yr−1(Nugis et al. 2007).
2MASS J00461632−7411135 (SMC IRS 94), also known as
MSX SMC 014, was classified as an R CrB candidate by
Kraemer et al. (2005), based on the IRS spectrum and near-
IR variability. This classification is supported by its 3–4=-
um spectrum from van Loon et al. (2008).
2MASS J00364631−7331351 (SMC IRS 95) is also known
as MSX SMC 029. PAH features in the IRS spectrum of this
source (Kraemer et al. 2006) and the spectral appearance of
the 3–4-µm wavelength range (van Loon et al. 2008) point
to a C-rich post-AGB star.
2MASS J00455394−7323411 (SMC IRS 96) is also known
as MSX SMC 036. Spectra from Groenewegen et al. (2009),
van Loon et al. (2008), and Sloan et al. (2006) all reveal
the presence of C2H2, demonstrating that this a C-rich
AGB star. Sloan et al. (2006) also note SiC and MgS dust
features in the IRS spectrum. OGLE-III (Soszy´nski et al.
2011) measure a p eriod of 553 days, and an I-band am-
plitude of 2.01 mag. It is also variable in the infrared
(Polsdofer et al. 2015). Groenewegen et al. (2009) find ˙
M=
3.6×10−6M⊙yr−1.
2MASS J00430590−7321406 (SMC IRS 97), also known
as MSX SMC 054, is a C-rich AGB star, as demonstrated
by spectra from Groenewegen et al. (2009), van Loon et al.
(2008), and Sloan et al. (2006), which all confirm the pres-
ence of C2H2. Sloan et al. (2006) also note SiC and MgS dust
features in the IRS spectrum. Groenewegen et al. (2009)
find ˙
M= 3.9×10−6M⊙yr−1. Its period is not known, al-
though it is an infrared variable (Polsdofer et al. 2015).
IRAS F00483−7347 (SMC IRS 98) is also known as S9 and
c
0000 RAS, MNRAS 000, 000–000
26 Paul M. E. Ruffle et al.
MSX SMC 055. IR spectra from Groenewegen et al. (2009)
and van Loon et al. (2008) indicate an M star, with spectral
type M8. Optical spectra show ZrO+H2O and TiO absorp-
tion (Groenewegen & Blommaert 1998). Variability infor-
mation (P= 1749 d, AmpI= 0.87 mag; Groenewegen et al.
2009), a Li-overabundance (Castilho et al. 1998), and Rb
enhancement (Garc´ıa-Hern´andez et al. 2009) also point to
an AGB star. Groenewegen et al. (2009) classify the star
as a Mira, and a candidate super-AGB star ( ˙
M= 5.3×
10−6M⊙yr−1). No maser emission has been detected
(van Loon et al. 2001; Marshall et al. 2004). We classify it
as an RSG by virtue of its Mbol=−7.3 mag. It is also in the
Riebel et al. (in prep.) list of infrared variables.
IRAS F00448−7332 (SMC IRS 99), also known as S6 or
MSX SMC 060 is known to be a carbon-rich AGB star. Spec-
tra from Groenewegen et al. (2009), van Loon et al. (2008),
and Sloan et al. (2006) all confirm the presence of C2H2.
Sloan et al. (2006) also note SiC and MgS dust features
in the IRS spectrum. Groenewegen et al. (2009) measure a
period of 429 days, a K-band amplitude of 0.55 mag, and
˙
M= 8.9×10−6M⊙yr−1. It is also variable in the infrared
(Polsdofer et al. 2015, Riebel et al. in prep.). Sloan et al.
(2006) note that its pulsation properties and photometry
make it look similar to R CrB stars, but its spectrum does
not support that classification. We classify it as an C-AGB
star, consistent with the literature.
2MASS J00485250−7308568 (SMC IRS 100), also known
as MSX SMC 066, was suggested to be a carbon star by
Raimondo et al. (2005) based on its near-IR colours, consis-
tent with our classification and that of Sloan et al. (2006)
as a carbon-rich AGB star. Although listed as a Mira by
Soszy´nski et al. (2011), there is some question regarding its
primary period, given as 519.5 days therein, but as 267 days
by Groenewegen (2004) with a secondary period of 512 days.
It is also in the Riebel et al. (in prep.) list of infrared vari-
ables.
2MASS J00592336−7356010 (SMC IRS 101), also known
as MSX SMC 093, was identified as a carbon-rich object
by Sloan et al. (2006), who noted it has a particularly weak
SiC emission feature. Soszy´nski et al. (2011) used the OGLE
light curve and near-infrared photometry to classify it as a
carbon-rich semi-regular variable with a primary period of
457 days. We classify it here as C-AGB.
2MASS J00450214−7252243 (SMC IRS 102), also known
as MSX SMC 105, was identified as a carbon star can-
didate by Tsalmantza et al. (2006) by its 2MASS near-IR
colours. Shortly thereafter, Sloan et al. (2006) found that its
IRS spectrum showed a moderately thick carbon-rich dust
shell. OGLE data show that it is a Mira with a period of
∼670 days (Groenewegen 2004; Soszy´nski et al. 2011). It is
also a known infrared variable (Polsdofer et al. 2015). We
classify it here as a C-AGB, consistent with the previous
works.
2MASS J00515018−7250496 (SMC IRS 103), also known
as MSX SMC 125, was identified as a carbon star by
Raimondo et al. (2005) based on its near-IR photome-
try. MACHO and OGLE both find a primary period of
∼460 days and Soszy´nski et al. (2011) call it a carbon-
rich Mira. This source is also known to vary in the in-
frared (Polsdofer et al. 2015, Riebel et al. in prep.). It
was not in the Sloan et al. (2006) sample of SMC carbon
star observations with the IRS due to contamination by
Massey SMC 21202 in the IRS slit. The IRS spectrum of
2MASS J00515018−725049 was recovered in the present re-
processing and is classified as a C-AGB, consistent with the
optical and near-IR data.
2MASS J00542228−7243296 (SMC IRS 104), also known
as MSX SMC 159, is classified as a carbon-rich AGB star
by Sloan et al. (2006), based on its IRS spectrum, its period
(560 days) and its luminosity (7470 L⊙). It is also known to
vary in the infrared (Riebel et al. in prep.). Kamath et al.
(2014) list this object as a candidate PN, but that is incon-
sistent with its firm C-AGB classification.
2MASS J00510074−7225185 (SMC IRS 105), also known
as MSX SMC 163, is classified as a carbon-rich AGB star
by Sloan et al. (2006), based on its IRS spectrum, its pe-
riod (660 days) and its luminosity (13,000 L⊙). This source
was also found to be infrared-variable (Polsdofer et al. 2015,
Riebel et al. in prep.).
IRAS 01039−7305 (SMC IRS 106), also known as 2MASS
J01053027−7249536 and MSX SMC 180, was first de-
tected with IRAS as an infrared source towards the SMC
(Schwering & Israel 1989). It was identified as being part
of an OB association by Battinelli (1991), and classi-
fied as a YSO candidate based its near-IR spectroscopy
(van Loon et al. 2008). This classification was confirmed us-
ing Spitzer spectroscopy (Oliveira et al. 2013). Here we clas-
sify it as YSO-2.
2MASS J00571098−7230599 (SMC IRS 107), also known
as MSX SMC 198, is classified as a carbon-rich AGB star
by Sloan et al. (2006), based on its IRS spectrum, its period
(500 days) and it luminosity (7810 L⊙). This source is also
known to vary in the infrared (Polsdofer et al. 2015, Riebel
et al. in prep.).
2MASS J00465078−7147393 (SMC IRS 108), also known
as MSX SMC 200, is classified as a carbon-rich AGB star
by Sloan et al. (2006), based on its IRS spectrum and its
luminosity (9130 L⊙).
2MASS J01060330−7222322 (SMC IRS 109), also known
as MSX SMC 232, is classified as a carbon-rich AGB star
by Sloan et al. (2006), based on its IRS spectrum, its period
(460 days) and its luminosity (7280 L⊙). It is an infrared
variable (Polsdofer et al. 2015, Riebel et al. in prep.).
HV 1375 (SMC IRS 110) is also known as MSX SMC 024. IR
spectra (this work, Groenewegen et al. 2009; van Loon et al.
2008) identify it as an M type AGB star. Groenewegen et al.
(2009) find a spectral type of M5, a period of 418 days, an I-
band amplitude of 0.11 mag, and ˙
M= 6.3×10−7M⊙yr−1.
Smith et al. (1995) detect a strong Li overabundance.
HV 11262 (SMC IRS 111), which is also known as MSX
SMC 067, is a red supergiant with an optical spectral
type of late K or early M (Massey 2002; Massey et al.
2009), and was first noted as a possible variable by
Payne-Gaposchkin & Gaposchkin (1966). This source is also
known to vary in the infrared (Polsdofer et al. 2015, Riebel
et al. in prep.). Its IRS spectrum is dominated by photo-
spheric emission, and the fine structure lines longward of
15 µm are probably contamination from a nearby source or
the extended emission seen in the neighborhood.
IRAS 00469−7341 (SMC IRS 112), also known as MSX
SMC 079, was identified by Bolatto et al. (2007) as a can-
didate YSO based on its IRAC and MIPS photometry. Van
Loon et al. (2008) detected H2O absorption as well as Pfγ
and Brαemission in a 3–4-µm spectrum, and noted it is lo-
c
0000 RAS, MNRAS 000, 000–000
Spitzer-IRS point source classification in the SMC 27
cated near the young cluster Bruck 48. Oliveira et al. (2013)
analyzed its IRS spectrum as part of an IRS study of SMC
YSOs and classified it with a group of early, embedded YSOs
with strong ice and silicate absorption, weak PAHs, and no
fine-structure lines. It is known to be an infrared variable
(Polsdofer et al. 2015).
RAW 631 (SMC IRS 113), also known as MSX SMC 134,
was classified as a carbon star from its optical spectrum
by Rebeirot et al. (1993). It also shows absorption features
from C2H2and HCN in the 3–4-µm region (van Loon et al.
2008), although its spectrum is somewhat atypical of the
other carbon stars in that sample. Kamath et al. (2014)
also list it as a carbon star. In contrast, the IRS spectrum
shows strong features from crystalline silicates at ∼19, 23,
27, and 33 µm, which are more typical of oxygen-rich objects.
Jones et al. (2012) analyse this dual chemistry source in
their sample of O-rich evolved stars, and suggest the strong
crystalline silicate features are indicative of dust process-
ing in a circumstellar disk, possibly around a binary system
(Barnbaum et al. 1991; Lloyd Evans 1991). In this work, we
classify it as O-AGB, because of the dominance of oxygen-
rich features in the Spitzer spectrum.
2MASS J00571814−7242352 (SMC IRS 114), also known
as MSX SMC 155, was classified as a R CrB candidate
by Tisserand et al. (2004), based on its EROS 2 opti-
cal lightcurve. From Spitzer spectroscopy, Kraemer et al.
(2005) confirmed that it is carbon-rich, with an almost
featureless mid-infrared spectrum, characteristic of R CrB
stars. It is known to vary in the infrared (Polsdofer et al.
2015).
HV 11417 (SMC IRS 115) was classified as an SMC M su-
pergiant by Elias et al. (1980), based on photometric and
spectroscopic observations. It was the first extragalactic red
supergiant ever identified. This source is also an infrared
variable (Polsdofer et al. 2015, Riebel et al. in prep.).
HV 12122 (SMC IRS 116) is an M-type AGB star (Spectral
Type: M5) with a period of 544 days and an I-band ampli-
tude of 1.43 mag (Groenewegen et al. 2009). They measure
a low value for ˙
Mof 2.7×10−8M⊙yr−1. The source is also
known to vary in the infrared (Polsdofer et al. 2015, Riebel
et al. in prep.). Smith et al. (1995) detect a Li overabun-
dance in the optical spectrum, indicating HBB. They also
detect TiO & ZrO, in the optical spectrum.
PMMR 34 (SMC IRS 117), which is also known as MSX
SMC 096, is a red supergiant (e.g. Prevot et al. 1983;
Elias et al. 1985; Massey 2002). Yang & Jiang (2012) found
it to be a semi-regular pulsator with a period of 381–388 days
using data from the ASAS project (Pojmanski 2002). Its IRS
spectrum shows weak silicate emission as well as PAH fea-
tures. There is no apparent extended emission in the region,
so the PAHs must be local to the source.
SkKM 71 (SMC IRS 118), also known as MSX SMC 109, is
one of the many red supergiants discovered by Sanduleak
in the Magellanic Clouds (Humphreys 1979; Elias et al.
1985; Sanduleak 1989). Using ASAS data (Pojmanski 2002),
Yang & Jiang (2012) found it to be a ‘long secondary pe-
riod’ variable with a period of ∼565 days. Its IRS spectrum
shows 9 and 18-µm silicate emission features as well as a
PAH feature at 11.3 µm. As with PMMR 34, there is no ob-
vious extended emission to contaminate the IRS slit so we
conclude that the PAHs are local to the RSG.
HV 2084 (SMC IRS 119) is a known red supergiant (e.g.
Prevot et al. 1983; Elias et al. 1985; Massey 2002).
HV 1652 (SMC IRS 120) was observed during an objective-
prism survey of the Small Magellanic Cloud by Prevot et al.
(1983). It was identified as a M0-1 supergiant.
2MASS J00463159−7328464 (SMC IRS 121), also known
as MSX SMC 018, is shown to be a Mira with P=
897 days and ∆I= 2.47 mag based on its OGLE-III light
curve (Soszy´nski et al. 2011). It is also an infrared vari-
able (Polsdofer et al. 2015). Groenewegen et al. (2009) clas-
sify it as M-type (SpT = M7) and measure ˙
M= 8.1×
10−6M⊙yr−1. van Loon et al. (2008) also classify the star
as M-type via 3–4-µm spectra, consistent with our classifi-
cation as O-AGB.
2MASS J00470552−7321330 (SMC IRS 122) is also known
as MSX SMC 033. Spectra from Groenewegen et al. (2009),
van Loon et al. (2008), and Sloan et al. (2006) all demon-
strate the carbon-rich AGB nature of this ob ject with
the presence of C2H2features. Sloan et al. (2006) also
note a SiC dust feature in the IRS spectrum. OGLE-III
(Soszy´nski et al. 2011) measure a period of 535 days, and
an I-band amplitude of 1.93 mag. Groenewegen et al. (2009)
find that ˙
M= 3.7×10−6M⊙yr−1. It is also variable in the
infrared (Riebel et al. in prep.). We classify this source as
C-AGB, consistent with previous studies.
2MASS J00433957−7314576 (SMC IRS 123), also known
as MSX SMC 044, is a C-rich AGB star. Spectra
from Groenewegen et al. (2009), van Loon et al. (2008),
and Sloan et al. (2006) all confirm the presence of C2H2.
Sloan et al. (2006) also note an SiC dust feature in the IRS
spectrum. OGLE-III (Soszy´nski et al. 2011) measure a pe-
riod of 440 days, and an I-band amplitude of 1.39 mag. This
source is also known to vary in the infrared (Polsdofer et al.
2015, Riebel et al. in prep.). Groenewegen et al. (2009) find
˙
M= 3.1×10−6M⊙yr−1. We classify this source as C-AGB,
consistent with previous studies.
2MASS J00424090−7257057 (SMC IRS 124), also known
as MSX SMC 062, is a C-rich AGB star. Spectra from
Groenewegen et al. (2009) and Sloan et al. (2006) con-
firm the presence of C2H2. Sloan et al. (2006) also notes
an SiC dust feature in the IRS spectrum. OGLE-III
(Soszy´nski et al. 2011) measure a period of 550 days, and
an I-band amplitude of 1.78 mag (Mira). Groenewegen et al.
(2009) measure that ˙
M= 1.8×10−6M⊙yr−1. We classify
this source as C-AGB, consistent with these earlier studies.
2MASS J00365671−7225175 (SMC IRS 125), also known
as MSX SMC 091, is an AGB star with a thick carbon-rich
dust shell (Sloan et al. 2006). They noted it has a partic-
ularly strong SiC emission feature for an SMC source but
no 26–30-µm feature. It has a very limited presence in op-
tical catalogues, with no detections blueward of Rband,
where it has a magnitude of ∼18.2 or 18.5 (Lasker et al.
2008; Monet et al. 2003, respectively).
2MASS J00514047−7257289 (SMC IRS 126), also known
as MSX SMC 142, was identified as a carbon star candidate
by Raimondo et al. (2005) from its near-IR photometry.
The OGLE light curve shows it is a Mira (Soszy´nski et al.
2011) with a period of ∼295 days (Groenewegen 2004;
Soszy´nski et al. 2011). It is also variable in the infrared
(Polsdofer et al. 2015, Riebel et al. in prep.). It is the weak-
est source in the Sloan et al. (2006) sample but clearly has
a carbon-rich dust spectrum in the IRS.
c
0000 RAS, MNRAS 000, 000–000
28 Paul M. E. Ruffle et al.
2MASS J00524017−7247276 (SMC IRS 127), also known
as MSX SMC 162, is classified as a carbon-rich AGB star
by Sloan et al. (2006), based on its IRS spectrum, its period
(520 days) and its luminosity (11480 L⊙). It is also known to
vary in the infrared (Polsdofer et al. 2015, Riebel et al. in
prep.).
2MASS J00531013−7211547 (SMC IRS 128), also known
as MSX SMC 202, is classified as a carbon-rich AGB star
by Sloan et al. (2006), based on its IRS spectrum and its lu-
minosity (11460 L⊙). This source is also an infrared variable
(Polsdofer et al. 2015).
2MASS J00561639−7216413 (SMC IRS 129), also known
as MSX SMC 209, is classified as a carbon-rich AGB star
by Sloan et al. (2006), based on its IRS spectrum, its period
(520 days) and its luminosity (16330 L⊙). It is also in the
Polsdofer et al. (2015) and Riebel et al. (in prep.) lists of
infrared variables.
2MASS J01080114−7253173 (SMC IRS 131), also NGC 419
LE 16, is a semi-regular variable located near the cluster
NGC 419. It was discovered by Lloyd Evans (1978) and clas-
sified as a carbon star based on colours. The classification is
confirmed from Spitzer spectroscopy (Lagadec et al. 2007).
The cluster is approximately 2 Gyr old (Kamath et al.
2010). The star shows several periods including a long
secondary one; the likely fundamental period is 416 days
(Soszy´nski et al. 2011). It is also variable in the infrared
(Polsdofer et al. 2015).
2MASS J01082495−7252569 (SMC IRS 134), also RAW
1553 and NGC 417 LE 18, is a well-studied carbon star in
the cluster NGC 419. It was first discovered by Lloyd Evans
(1978) and spectroscopically observed by Rebeirot et al.
(1993). The semiregular variable (Soszy´nski et al. 2011) has
a dominant period of 181 days (Kamath et al. 2010).
2MASS J01082067−7252519 (SMC IRS 135), also NGC
419 LE 27, was discovered by Lloyd Evans (1978). The
semiregular variable has a dominant period of 311 day
(Soszy´nski et al. 2011). It shows the characteristic carbon
star bands in the Spitzer SL spectrum (Lagadec et al. 2007).
2MASS J00353726−7309561 (SMC IRS 136) was discov-
ered as a variable by Glen Moore (see Lagadec et al. 2007)
using UK schmidt plates. It is classified as a carbon star on
the basis of both colours (Raimondo et al. 2005) and Spitzer
spectra (Lagadec et al. 2007). A C/O ratio close to unity is
indicated by the peculiar 11-µm feature, lack of C2H2fea-
tures (Lagadec et al. 2007), and high resolution spectra of
Abia et al. (2011).
PMMR 52 (SMC IRS 137), is a well-studied SMC
RSG. Massey & Olsen (2003) find Mb ol=−8.8 mag, vrad =
159.1 km s−1, and a spectral type of K5-7 I. The star
shows low-amplitude variability with a period of 483 days
(Yang & Jiang 2012) and has silicate dust (Lagadec et al.
2007). It is also an infrared variable (Polsdofer et al. 2015).
Note that the star should not be be confused with the
nearby carbon Mira J005304.7−730409 (van Loon et al.
2008) which was the original but missed target of the Spitzer
spectroscopy.
2MASS J00545410−7303181 (SMC IRS 139) is a 541-day
Mira variable (Soszy´nski et al. 2011), classified as a car-
bon star on the basis of optical and Spitzer spectroscopy
(Rebeirot et al. 1993; Lagadec et al. 2007). The 13.7-µm
C2H2absorption features are absent. It is also in the
Polsdofer et al. (2015) and Riebel et al. (in prep.) lists of
infrared variables.
2MASS J00545075−7306073 (SMC IRS 140) is classified as
a Mira with a period of 430 days (Soszy´nski et al. 2011), and
it is also an infrared variable (Polsdofer et al. 2015, Riebel et
al. in prep.). It is classified as a carbon star based on pho-
tometry (Raimondo et al. 2005) and Spitzer spectroscopy
(Lagadec et al. 2007).
2MASS J01015458−7258223 (SMC IRS 142) is identified as
a carbon star based on the absorption bands in the Spitzer
spectrum (Lagadec et al. 2007). Soszy´nski et al. (2011) re-
port a period of 339 days. The source is also known to vary
in the infrared (Polsdofer et al. 2015, Riebel et al. in prep.).
LEGC 105 (SMC IRS 143) is located near a small clus-
ter, Bruck 80. The age of the cluster is 5 ×108yr
(Chiosi et al. 2006). The star was discovered as a 310-day
variable by Lloyd Evans et al. (1988) (#105 in their paper).
Polsdofer et al. (2015) and Riebel et al. (in prep.) also find
it to be an infrared variable. The Spitzer spectrum classi-
fies it as a carbon star but there is little or no dust excess
(Lagadec et al. 2007).
2MASS J00572054−7312460 (SMC IRS 144) is a 350-day
Mira variable (Soszy´nski et al. 2011). It is also known to
vary in the infrared (Polsdofer et al. 2015, Riebel et al. in
prep.). Lagadec et al. (2007) find the typical carbon-star
bands in the Spitzer spectrum whilst Raimondo et al. (2005)
classify it as a carbon star based on infrared colours.
2MASS J00555464−7311362 (SMC IRS 145), also RAW
960, is a 315-day Mira variable (Soszy´nski et al. 2011), clas-
sified as a carbon star based on optical photometry and spec-
troscopy (Rebeirot et al. 1993), using the 516 nm C2band.
Lagadec et al. (2007) find little evidence for cool dust but
strong molecular absorption bands of C2H2. This source is
also an infrared variable (Polsdofer et al. 2015, Riebel et
al. in prep.).
IRAS 00554−7351 (SMC IRS 146) was identified by
Whitelock et al. (1989) as a very long period variable near
the tip of the AGB. Soszy´nski et al. (2011) report a period
of 610 days. The Spitzer spectra (this work; Lagadec et al.
2007) show the typical carbon-star features.
NGC 419 IR 2 (SMC IRS 147) is located in a crowded region
of NGC 419. Tanab´e et al. (1997) first discovered the self-
obscured infrared source and the high mass-loss rate was
confirmed by van Loon et al. (2005). The p eriod is 381 days
(Kamath et al. 2010). It is also in the Polsdofer et al. (2015)
of infrared variables. We classify it as C-AGB.
NGC 419 IR 1 (SMC IRS 148), also known as 2MASS
J01081296−7252439, is a large-amplitude (Kamath et al.
2010), 461-day Mira variable (Soszy´nski et al. 2011) first re-
ported by Tanab´e et al. (1997). It is classified as carbon-
rich based on the Spitzer spectra (this work; Lagadec et al.
2007), and is also known to vary in the infrared
(Polsdofer et al. 2015).
AzV 404 (SMC IRS 149) is a B2.5 yellow supergiant
(Lennon 1997). It has been modelled to have a luminosity
of 174,000 L⊙and light reddening of E(B−V) = 0.05 mag
(Dufton et al. 2000). We have classified it as STAR, due to
the absence of emission features in the IR.
LHA 115-N38 (SMC IRS 153), also known as SMP SMC 13,
is a round PN with a radius of 0.19 arcsec (Stanghellini et al.
2003a). The dust features point to a carbon-rich chemistry,
and the object shows intermediate excitation lines. The tem-
c
0000 RAS, MNRAS 000, 000–000
Spitzer-IRS point source classification in the SMC 29
perature of the dust continuum is derived to be Tcont =
190 K (Stanghellini et al. 2007). The abundance of carbon
is slightly elevated (Stanghellini et al. 2009), and LHA 115-
N 38 is known to contain fullerenes (Garc´ıa-Hern´andez et al.
2011).
LHA 115-N 40 (SMC IRS 154), also known as SMP SMC
14, is a round PN with a radius of 0.42 arcsec, showing some
internal structure (Stanghellini et al. 2003a). The Spitzer
spectrum reveals carbon-rich dust features and high exci-
tation lines, and a dust temperature of Tcont = 150 K can
be derived (Stanghellini et al. 2007).
LHA 115-N 43 (SMC IRS 155), which is also known as
SMP SMC 15, is a round PN with a radius of 0.17 arcsec
(Stanghellini et al. 2003a). The Spitzer spectrum shows
carbon-rich dust features, intermediate excitation lines, a
dust continuum with Tcont = 190 K, and PAH-related emis-
sion features at 15-21 µm. The SiC feature is unusually
broad, and the spectrum is similar to that of SMP SMC 18
and 20 (Stanghellini et al. 2007). LHA 115-N 43 is known
to contain fullerenes (Garc´ıa-Hern´andez et al. 2011).
LHA 115-N 42 (SMC IRS 156), also known as SMP
SMC 16, is an elliptical PN with a radius of 0.18 arcsec
(Stanghellini et al. 2003a). The IRS spectrum shows carbon-
rich dust, and low excitation lines, while a dust temper-
ature of Tcont = 180 K can be derived (Stanghellini et al.
2007). The object is known to contain fullerenes
(Garc´ıa-Hern´andez et al. 2011). All of this is consistent with
our classification as C-PN.
LHA 115-N 44 (SMC IRS 157) is also known as SMP SMC
17. It is an elliptical PN with a radius of 0.25 arcsec, with a
faint detached halo (Stanghellini et al. 2003a). The carbon-
rich nature is revealed by its IRS spectrum, due to the
presence of carbon-rich dust. Intermediate excitation lines
are present and the dust temperature is Tcont = 160 K
(Stanghellini et al. 2007).
LHA 115-N 47 (SMC IRS 158), also known as SMP SMC
18, is an unresolved PN (Stanghellini et al. 2003a). It is
carbon-rich in nature, and shows intermediate excitation
lines. The dust temperature is derived to be Tcont = 170 K
(Stanghellini et al. 2007). The N and O abundances are
slightly low (Shaw et al. 2010), and it contains fullerenes
(Garc´ıa-Hern´andez et al. 2011).
Lin 239 (SMC IRS 159), also known as Jacoby SMC 20 and
SMP SMC 19 is a round PN with a radius of 0.30 arcsec,
showing some outer structure (Stanghellini et al. 2003a). It
is carbon-rich in nature and shows very high excitation lines.
The dust temperature is measured to be Tcont = 150 K
(Stanghellini et al. 2007).
LHA 115-N 54 (SMC IRS 160), also known as SMP SMC
20, is an unresolved PN (Stanghellini et al. 2003a), with
a carbon-rich nebula showing intermediate excitation lines
(Stanghellini et al. 2007). These last authors have also de-
rived the dust temperature to be Tcont = 250 K, which is
very high, and suggest that it is one of the least evolved
PNe of their sample. LHA 115-N 54 shows somewhat low
N, O, Ne, S, and Ar abundances (Shaw et al. 2010), and
may also contain fullerenes (Garc´ıa-Hern´andez et al. 2011),
although Sloan et al. (2014) could not confirm this claim.
Lin 343 (SMC IRS 161), also known as SMP SMC 23
or Jacoby SMC 26, is a bipolar core PN with a radius
of 0.30 arcsec (Stanghellini et al. 2003a). The IR spectrum
shows intermediate excitation lines, and a dust continuum
with a temperature of Tcont = 150 K (Stanghellini et al.
2007).
Lin 357 (SMC IRS 162), also known as SMP SMC 25, is an
elliptical PN with a radius of 0.19 arcsec (Stanghellini et al.
2003a). The IRS spectrum reveals an O-rich chemistry and
shows very high excitation lines, on top of a dust continuum
of Tcont = 130 K (Stanghellini et al. 2007). The ob ject shows
a low carbon abundance (Stanghellini et al. 2009). The pro-
genitor was probably a high-mass star (Villaver et al. 2004),
causing HBB.
Lin 430 (SMC IRS 163), also known as SMP SMC 26,
is a point-symmetric PN with a radius of 0.28 arcsec
(Stanghellini et al. 2003a). Very high excitation lines are
present in the IR, on top of a dust continuum of Tcont =
130 K (Stanghellini et al. 2007). We classify it as C-PN.
LHA 115-N 87 (SMC IRS 164), also known as SMP SMC
27, is a round PN with a radius of 0.23 arcsec, and an at-
tached outer halo (Stanghellini et al. 2003a). The IRS spec-
trum shows carbon-rich dust features and intermediate ex-
citation lines, on top of a dust continuum of Tcont = 180 K
(Stanghellini et al. 2007). Fullerenes may also be present in
this source (Garc´ıa-Hern´andez et al. 2011), although this is
not confirmed by Sloan et al. (2014).
LHA 115-N2 (SMC IRS 165), also known as SMP SMC
2 or Lin 14, is a round PN with radius of 0.25 arcsec
(Stanghellini et al. 2003a). The IRS spectrum shows carbon-
rich dust and very high excitation lines on a dust continuum
of Tcont = 160 K (Stanghellini et al. 2007).
LHA 115-N 5 (SMC IRS 166), or SMP SMC 5 or Line 32, is
a round PN with a radius of 0.31 arcsec (Stanghellini et al.
2003a). The IRS spectrum shows carbon-rich dust and very
high excitation lines, on a dust continuum of Tcont = 180 K
(Stanghellini et al. 2007).
LHA 115-N 7 (SMC IRS 167), also SMP SMC 8 or Lin 43, is
a round PN with a radius of 0.23 arcsec (Stanghellini et al.
2003a). In the infrared, intermediate excitation lines sit on
a featureless continuum of Tcont = 160 K (Stanghellini et al.
2007).
BFM 1 (SMC IRS 170). The presence of the LaO
band at 0.79 µm indicates that BFM 1 is an S star
(Blanco et al. 1981). It is kn own to show H αemis-
sion (Meyssonnier & Azzopardi 1993), and its MACHO
lightcurve is used to derive a period of 394–400 days
(Raimondo et al. 2005; van Loon et al. 2008; Sloan et al.
2008). OGLE variability data also exist (Soszy´nski et al.
2011). It is also an infrared variable (Riebel et al. in prep.).
BFM 1 is observed twice with Spitzer IRS (2.ST, 2.NO;
Sloan et al. 2008) and the spectrum shows ZrO and LaO
bands, and a dust emission feature at 13–14 µm, which
has been attributed to SiS (Sloan et al. 2011). The fitted
blackbody temperature is 1460 ±110 K or 1160 ±10 K
(Sloan et al. 2008). We have classified this as OTHER - S
Star.
HV 1963 (SMC IRS 171) is a known LPV, with a spectral
type consistent with an AGB star and a period of 330 days
(Catchpole & Feast 1981; Wood et al. 1983), in agreement
with our O-EAGB classification. It is also known to vary in
the infrared (Polsdofer et al. 2015). HV 1963 appears to be
enhanced in Lithium and s process elements, while other-
wise having low metallicity (Smith & Lambert 1989). The
high Lithium abundance, indicative of hot bottom burning
in 4–8-M⊙AGB stars, is confirmed by Smith & Lambert
c
0000 RAS, MNRAS 000, 000–000
30 Paul M. E. Ruffle et al.
(1990), Plez et al. (1993) and Smith et al. (1995). The red
spectrum shows moderately strong TiO and weak CN and
ZrO bands, pointing towards carbon dredge up, and possi-
bly envelope burning (Brett 1991). These authors also esti-
mate that C/O ratio is around 0.4–0.8. The spectral type of
HV 1963 is established to be M4.5s..., with Teff = 3350 K,
log g=−0.27 and [Fe/H] = −0.43 (Soubiran et al. 2010).
HV 1963 was observed twice with Spitzer IRS. Sloan et al.
(2008) report a spectral classification of 1.N:O(:) and fit a
blackbody temperature of 2160 ±120 K or 1990 ±50 K. A
revised period of 249 days is derived from the OGLE data
(Sloan et al. 2008). The dust mass loss rate is found to be
10−9.8M⊙yr−1(Boyer et al. 2012).
HV 11329 (SMC IRS 172) is reported to be a variable O-rich
AGB star (Catchpole & Feast 1981; Wood et al. 1983), with
a period of 390 days, in agreement with our classification of
O-EAGB. Lloyd Evans (1985) revised the pulsational pe-
riod to 380 days. It is also in the Polsdofer et al. (2015) and
Riebel et al. (in prep.) lists of infrared variables. Strong Li i
absorption at 6707 and 8126 ˚
A indicates hot bottom burn-
ing (Smith & Lambert 1990; Plez et al. 1993; Smith et al.
1995). The effective temperature of this member of NGC 292
is found to be Teff = 3600 K, with log g=−0.05 and [Fe/H]
=−0.37 (Soubiran et al. 2010). Sloan et al. (2008) assign a
spectral classification of 1.NO, and fit a blackbody of 1600
±80 K. The MACHO data indicate a period of 377 days
(Sloan et al. 2008; Yang & Jiang 2012) and OGLE variabil-
ity data also exist for this source (Soszy´nski et al. 2011).
2MASS J00445256−7318258 (SMC IRS 175). Variability
data are available for this object in the OGLE and MACHO
surveys, and a period of 158 days has been derived from
the OGLE data (Groenewegen 2004), while Raimondo et al.
(2005) arrive at a period of 129 days using the MACHO data.
We classify this object as an O-AGB star. The infrared spec-
trum is dominated by crystalline silicate features at ∼19,
23, 28, and 33 µm originating from the circumstellar dust
shell, and we classify this object as an O-AGB star, despite
the presence of the 7.5 and 13.7 µm absorption bands due
to C2H2, pointing towards a carbon-rich central star. Like
RAW 631, this object shows a dual chemistry (see also Krae-
mer et al. in prep.).
PMMR 24 (SMC IRS 176), also known as Massey SMC
11939, is known to be a RSG (e.g. Bonanos et al.
2010; Yang & Jiang 2012). Several (inconsistent) radial
velocity measurements exist (Maurice et al. 1987, 1989;
Massey & Olsen 2003), and the period of 352 days is de-
termined using MACHO data (Cioni et al. 2003). Atmo-
spheric modeling of the optical spectra yields Teff = 4025 K,
AV= 1.05, log g= 0.0, and R= 750 R⊙. Polsdofer et al.
(2015) found it to be variable in the infrared.
BMB-B 75 (SMC IRS 177) is a dust enshrouded O-
rich AGB star of spectral type M6.0 (Blanco et al. 1980),
showing long period variability in both the MACHO
(Raimondo et al. 2005) and OGLE surveys (Groenewegen
2004; Soszy´nski et al. 2011). It is also variable in the infrared
(Polsdofer et al. 2015, Riebel et al. in prep.). SiO absorption
is seen in the NIR spectroscopy (van Loon et al. 2008). This
object has also been observed with Spitzer’s MIPS-SED, and
the data show a rising continuum, indicative of cold dust (42
±2 K), and no emission lines (van Loon et al. 2010).
IRAS F01066−7332 (SMC IRS 178) is a dust en-
shrouded oxygen-rich AGB star of spectral type M8
(Groenewegen & Blommaert 1998; van Loon et al. 2008),
in agreement with our classification of O-AGB. SED
fitting with a dusty circumstellar shell indicates that
its luminosity is 25,000 L⊙, and the mass loss rate is
5.0×10−7M⊙yr−1(Groenewegen et al. 2000). A search for
SiO using NIR spectroscopy does not yield any results
(van Loon et al. 2008). The source is also known as a long
period variable (Soszy´nski et al. 2011), and is also known to
vary in the infrared (Polsdofer et al. 2015).
RMC 50 (SMC IRS 193), also known as LHA 115-S 65,
SMC V2364, and IRAS 01432−7455, is a B[e] supergiant,
classified between B2 and B9, with Teff = 17,000 K and
L= 500,000 L⊙(Ardeberg & Maurice 1977; Zickgraf et al.
1986; Zickgraf 2000; Cidale et al. 2001; Kraus et al. 2010;
Bonanos et al. 2010). Although the star is only slightly
variable, the circumstellar environment appears very dy-
namic, with 2.2-µm CO emission appearing during 2011
(Oksala et al. 2012).
NGC 362 SAW V16 (SMC IRS 195) is not located in the
SMC, but rather a foreground object. It is a long-period vari-
able (V16 designation from Hogg; see Lloyd Evans 1983b)
in the Galactic globular cluster NGC362 ([Fe/H] = −1.33;
Shetrone & Keane 2000), hence a low-mass AGB star or a
tip-RGB star. Lloyd Evans (1983b) detected significant vari-
ations in the strength of the TiO bands during the pulsa-
tion cycle equivalent to spectral type variations K4–M4. He
also detected hydrogen emission, presumably due to pulsa-
tion shocks; McDonald & van L oon (2007) showed the H α
to be in self-absorption in an ´
Echelle spectrum, at a spec-
tral type K5.5. Lloyd Evans (1983a) determined a period of
135 days (138 days in Sloan et al. 2010) and an amplitude
∆V= 2.3 mag (similar to that of Mira variables), and con-
firmed cluster membership on the basis of radial velocity
measurements (cf. McDonald & van Loon 2007). It is also
known to be an infrared variable (Polsdofer et al. 2015). We
note that it should be an O-EAGB, but rather classify it is
as OTHER, since it is a foreground object.
HV 206 (SMC IRS 196) is a foreground star, rather than
an SMC object. It is a long-period variable (Sawyer 1931)
in the Galactic globular cluster NGC362 ([Fe/H] = −1.33;
Shetrone & Keane 2000), hence a low-mass AGB star or a
tip-RGB star (cf. Frogel et al. 1983). Lloyd Evans (1983b)
detected modest variations in the strength of the TiO bands
during the pulsation cycle. He also detected hydrogen emis-
sion, presumably due to pulsation shocks (cf. Smith et al.
1999). The pulsations are semi-regular with periods quoted
of 90 days (Lloyd Evans 1983a); 89 days (Sloan et al. 2010);
105 days (Lebzelter & Wood 2011). It has been found to be
lithium rich by Smith et al. (1999). Although it is an O-
EAGB, we classify this source as OTHER, since it is also a
foreground object.
Massey SMC 5822 (SMC IRS 197), is known as B4 in the
sample of Sheets et al. (2013) and Adams et al. (2013), who
are studying OB-type stars with an 24 or 70 µm excess de-
tected by MIPS indicative of dust emission. This star is
also known as source #5822 by Massey (2002), and is as-
signed a group identification number of 29 in the OB sam-
ple table (Table 4) of Oey et al. (2004). It has spectral type
O9 (Sheets et al. 2013), and Adams et al. (2013) determine
MV=−4.10 mag. We classify it as OTHER: dusty OB star.
Massey SMC 7776 (SMC IRS 198), corresponds to B9 in the
sample of infrared excess emission stars (Sheets et al. 2013;
c
0000 RAS, MNRAS 000, 000–000
Spitzer-IRS point source classification in the SMC 31
Adams et al. 2013). Adams et al. (2013) determine MV=
−3.87 mag and Evans et al. (2004b) assign a sp ectral type
of B0 V. We classify it as OTHER: dusty OB star.
2MASS J00465728-7318087 (SMC IRS 199) is entry B11
in the sample of Sheets et al. (2013); Adams et al. (2013)
of MIPS-24 or MIPS-70 excess emission stars. Adams et al.
(2013) determine MV=−2.95 mag. We classify it as
OTHER: dusty OB star.
2MASS J00471901-7307110 (SMC IRS 200) is B14 in the
sample of infrared excess emission stars (Sheets et al. 2013;
Adams et al. 2013). Adams et al. (2013) determine MV=
−4.52 mag, and the spectral type is thought to be B0–B2
(Sheets et al. 2013). We classify it as OTHER: dusty OB
star.
Massey SMC 9114 (SMC IRS 201) is also known as source
B21 in the infrared excess sample of Sheets et al. (2013) and
Adams et al. (2013), as source 2dFS5016 (Bonanos et al.
2010), as OGLE 04.130984 (Evans et al. 2004b), and as
source 01507 by Parker et al. (1998). Adams et al. (2013)
determine MV=−5.00 mag, Evans & Howarth (2008) re-
port a radial velocity of 150 ±6 km s−1and Evans et al.
(2004b) assign a spectral type of B1–2 II. We classify it as
OTHER: dusty OB star.
Massey SMC 9265 (SMC IRS 202), also known as OGLE
SMC-SC4 175188, is source B24 in the sample of OB
stars with infrared excess (Sheets et al. 2013; Adams et al.
2013). Adams et al. (2013) determine MV=−3.56 mag and
Evans et al. (2004b) assign a spectral type of B1–5 III.
Wyrzykowski et al. (2004) report this object is part of an
eclipsing binary system with a period of P=1.3243 days. We
classify this object as OTHER: dusty OB star.
SSTISAGEMA J004752.26-732121.8 (SMC IRS 203) is en-
try B26 in the list of OB stars with an infrared excess
(Sheets et al. 2013; Adams et al. 2013). Adams et al. (2013)
determine MV=−3.93 mag, and the spectral type is
thought to be B0–B2 (Sheets et al. 2013). We classify this
source as OTHER: dusty OB star.
Massey SMC 10129 (SMC IRS 204) is entry B29 in the sam-
ple of OB stars with an infrared excess (Sheets et al. 2013;
Adams et al. 2013), and is assigned a group identification
number of 50 in the OB sample table (Table 4) of Oey et al.
(2004). Adams et al. (2013) determine MV=−5.04 mag,
and the spectral type is thought to be B0 (Sheets et al.
2013). We classify this source as OTHER: dusty OB star.
2MASS J00483000-7318096 (SMC IRS 205) is entry B34 in
the sample of OB stars with an infrared excess (Sheets et al.
2013; Adams et al. 2013). The spectral type is thought to be
B0 (Sheets et al. 2013). We classify this source as OTHER:
dusty OB star.
Massey SMC 22613 (SMC IRS 206) corresponds to B83 in
the sample of OB stars with an infrared excess (Sheets et al.
2013; Adams et al. 2013). Adams et al. (2013) did not ana-
lyze this source since it is spatially resolved by Spitzer-IRS.
Evans et al. (2004b) assign a spectral type of B1-5 III, while
Evans & Howarth (2008) report a radial velocity of 165 ±
6 km s−1. We classify this source as OTHER: dusty OB star.
Massey SMC 28845 (SMC IRS 207), is entry B96 in the
sample of OB stars with an infrared excess (Sheets et al.
2013; Adams et al. 2013). The spectral type is thought to
be B0, and the star is known to be part of an eclipsing
binary system (Sheets et al. 2013). We classify this source
as OTHER: dusty OB star.
NGC 330 ELS 57 (SMC IRS 208), also known as object
B100 in the sample of Sheets et al. (2013) and Adams et al.
(2013); SMC5 009833 (Bonanos et al. 2010); and Massey
SMC 31632, although the Spitzer spectrum is extracted ∼1
arcsec away from the position of NGC 330 ELS 57. Accord-
ing to Evans et al. (2006), ELS 57, located 7.70 arcmin away
from the center of NGC 330, is of spectral type B0.5V and
has a radial velocity of 124 ±4 km s−1. Hunter et al. (2008)
assign the following stellar parameters to this star: Teff =
29,000 K, log g= 4.15, L= 104.34 L⊙, projected rotational
velocity vsini= 104 km s−1, and M= 13 M⊙. Hunter et al.
(2009) determine an atmospheric microturbulent velocity for
the star of 5 km s−1, and abundances of 8.01 ±0.18 dex for
Oxygen, 6.96 ±0.26 for Magnesium, and <7.48 ±0.29 for
Nitrogen. In the study by K¨ohler et al. (2012) this star is
known as S27, and they assign a main sequence lifetime
of 13.3 Myr, an inclination angle of sin iN= 0.33, and a
10.2 Myr isochrone age. Adams et al. (2013) determine an
absolute Vmagnitude, MV, of −3.36 mag. We classify this
object as OTHER: dusty OB star, based on these studies.
Massey SMC 32159 (SMC IRS 209), is entry B102 in the
sample of dusty OB stars from Sheets et al. (2013) and
Adams et al. (2013), and it is assigned a group identification
number of 195 in the OB sample table (Table 4) of Oey et al.
(2004). Adams et al. (2013) determine MV=−4.43 mag,
while Sheets et al. (2013) assing a spectral type of O9.
2MASS J00561161−7218244 (SMC IRS 210) is entry B112
in the sample of OB stars with a far-infrared excess
(Sheets et al. 2013; Adams et al. 2013). The star is known
to be part of an eclipsing binary system with a period of
4.48 days (Bayne et al. 2002; Faccioli et al. 2007). We clas-
sify this source as OTHER: dusty OB star.
AzV 216 (SMC IRS 211) also known as Massey SMC 44984,
is entry B137 in the sample of OB stars with an infrared
excess (Sheets et al. 2013; Adams et al. 2013). The spec-
tral type is thought to be B1–3II (Evans et al. 2004b) or
B1 (Sheets et al. 2013), and the star is known to be part
of an eclipsing binary system with a period of 1.84 days
(Faccioli et al. 2007). We classify this source as OTHER:
dusty OB star.
Massey SMC 50031 (SMC IRS 212) is entry B148 in the
sample of OB stars with an infrared excess (Sheets et al.
2013; Adams et al. 2013). The spectral type is thought to be
B0 (Sheets et al. 2013). We classify this source as OTHER:
dusty OB star.
Massey SMC 54281 (SMC IRS 213) is entry B154 in the
sample of OB stars with an infrared excess (Sheets et al.
2013; Adams et al. 2013). The spectral type is thought to be
B1 (Sheets et al. 2013). We classify this source as OTHER:
dusty OB star.
Massey SMC 55094 (SMC IRS 214) is entry B159 in the
sample of OB stars with an infrared excess (Sheets et al.
2013; Adams et al. 2013). The spectral type is thought to be
B0 (Sheets et al. 2013). We classify this source as OTHER:
dusty OB star.
Massey SMC 55634 (SMC IRS 215) is also known as B161 in
the sample of Sheets et al. (2013) and Adams et al. (2013).
The spectral type of this object is B0 (Sheets et al. 2013).
Adams et al. (2013) did not analyze this source since it
is spatially resolved by Spitzer-IRS, and there is a bright
source nearby in its IRS data. We classify this source as
OTHER: dusty OB star.
c
0000 RAS, MNRAS 000, 000–000
32 Paul M. E. Ruffle et al.
Massey SMC 60439 (SMC IRS 216) is entry B182 in the
sample of Sheets et al. (2013) and Adams et al. (2013), and
it is assigned a group identification number of 391 in the OB
sample table (Table 4) of Oey et al. (2004). Adams et al.
(2013) determine MV=−4.98 mag, while Sheets et al.
(2013) determine a spectral type of B0. We classify this as
OTHER: dusty OB star.
Massey SMC 67470 (SMC IRS 217) is entry B188 in the
sample of Sheets et al. (2013) and Adams et al. (2013). It is
assigned a group identification number of 445 in the OB sam-
ple table (Table 4) of Oey et al. (2004). Adams et al. (2013)
determine MV=−3.97 mag, while Sheets et al. (2013) be-
lieve that this is a Be star with weak H αabsorption. We
group it in the OTHER: dusty OB star category.
Massey SMC 77248 (SMC IRS 218) is entry B193 in the
sample of OB stars with an infrared excess (Sheets et al.
2013; Adams et al. 2013). The spectral type is thought to be
B0 (Sheets et al. 2013). We classify this source as OTHER:
dusty OB star.
Massey SMC 25387 (SMC IRS 219) is entry B87 in the sam-
ple of OB stars with a MIPS far-infrared excess (Sheets et al.
2013; Adams et al. 2013). It is assigned a group identifi-
cation number of 149 in the OB sample table (Table 4)
of Oey et al. (2004). Adams et al. (2013) determine MV=
−4.63 mag, while Sheets et al. (2013) its sp ectral type to b e
B0. We classify this source as OTHER: dusty OB star.
Massey SMC 55681 (SMC IRS 225) is listed as an M3
star by Elias et al. (1985) and M0–M1 in the catalogue
of Massey & Olsen (2003). The latter authors also calcu-
late Mbol=−10.53 mag, which supports our classification
of RSG. Polsdofer et al. (2015) also found it to vary in the
infrared.
Massey SMC 10889 (SMC IRS 226) was confirmed to be
a RSG in the SMC through high-accuracy radial velocity
measurements by Massey & Olsen (2003). A spectral type
of M0 Ia was assigned by Elias et al. (1985) and it is listed
as having K7 I spectral type by Massey & Olsen (2003). This
all supports our classification of RSG.
Massey SMC 11709 (SMC IRS 227). We classify this object
as a RSG, in agreement with Massey & Olsen (2003).
Massey SMC 46662 (SMC IRS 228) was identified as a late-
type RSG by Levesque et al. (2007) due to the significant
differences in the spectral types (M2 I to K2–3 I) and ef-
fective temperatures over short timescales. Its location in
the Hayashi forbidden zone of the H-R diagram indicates
the star is no longer in hydrostatic equilibrium and exhibits
considerable variability in Vmagnitudes. This supports our
classification of RSG. It is also known to vary in the infrared
(Polsdofer et al. 2015), and an X-SHOOTER spectrum is
available (Chen et al. 2014).
Massey SMC 52334 (SMC IRS 229). The preliminary
spectral type assigned by Elias et al. (1985) is M0 Iab,
and this object is also included in the RSG catalogue of
Massey & Olsen (2003) who list the spectral class as K7 I
and give Mbol= -8.15 mag. This is all in agreement with our
classification of RSG. An X-SHOOTER spectrum of this
object has been obtained (Chen et al. 2014).
HV 2232 (SMC IRS 230) is assigned a spectral type of
M2 in the catalogue of supergiants by Elias et al. (1985)
and Levesque et al. (2007). However, we classify this ob-
ject as O-AGB, based on the bolometric luminosity. An
X-SHOOTER spectrum of this object has been obtained
(Chen et al. 2014).
HV 11423 (SMC IRS 231) is an unstable cool supergiant
that was found by (Massey et al. 2007) to have varied its
spectral type between K0–1 I and M4.5–5 I on a timescale
of a few years. It was originally classified as an M0 super-
giant by Humphreys (1979) and Elias et al. (1985) and listed
by Massey & Olsen (2003) as a RSG in the SMC. We also
classify it as RSG.
Massey SMC 55188 (SMC IRS 232). Massey & Olsen (2003)
classify this source as a RSGs in the SMC, and it is also
identified as an unstable cool RSG with a spectral type (M2
I–4.5 I) by Levesque et al. (2007). We classify this object
as RSG. It is in the Polsdofer et al. (2015) list of infrared
variables, and an X-SHOOTER spectrum has been obtained
(Chen et al. 2014).
AzV 456 (SMC IRS 234), also known as Sk 143 (Sanduleak
1968), is a O9.5 or B0–1 yellow supergiant with Teff
= 23,000 – 30,000 K and L= 950,000 L⊙. Its spectral
type was previously thought to be even earlier (O8 II:
Smith Neubig & Bruhweiler 1997). The star is significantly
reddened by interstellar dust to E(B−V)≈0.37 mag,
of which ∼0.18 mag is attributed to foreground Galac-
tic dust, and hence has been used extensively to study
the intervening interstellar medium (Lequeux et al. 1982;
Prinja 1987; Thompson et al. 1988). The object shows a
wind with a terminal velocity of 1450 km s−1and ˙
M=
7×10−7M⊙yr−1(Prinja 1987; Evans et al. 2004a). Mem-
bership of the SMC is confirmed on the basis of its heliocen-
tric radial velocity vhel = 166 ±7 km s−1(Evans & Howarth
2008). Its proper motion has been measured at ≈2σsignif-
icance (µα= 6.7±3.2 mas yr−1,µδ=−5.6±3.1 mas yr−1;
Zacharias et al. 2004).
NGC 346 MPG 293 (SMC IRS 235) is a B3 Ia
(Azzopardi & Vigneau 1982), B1 Ia (Bouchet et al. 1985) or
B2 Ia (Smith Neubig & Bruhweiler 1997) supergiant in the
young massive cluster N GC 346. It has a relatively slow line-
driven wind (v∞≈900 km s−1; Prinja 1987), attributed to
the low metal content.
AzV 23 (SMC IRS 236) is a B3 Ia (Azzopardi & Vigneau
1982; Lennon 1997) yellow supergiant, first catalogued as
Sk 17 (Sanduleak 1968). Membership of the SMC is con-
firmed on the basis of its heliocentric radial velocity vhel =
178 km s−1(Neugent et al. 2010, who derived a spectral type
of B2 I). It has been modelled to have a luminosity of
230,000 L⊙and moderate reddening of E(B−V) = 0.21 mag
(Dufton et al. 2000).
IRAS 00350-7436 (SMC IRS 238), also known as LI-LMC
5, is a carbon-rich, high luminosity object (Mbol =−6.564
–−6.82 mag; Whitelock et al. 1989; van Loon et al. 1998;
Tsalmantza et al. 2006). Zijlstra et al. (1996) designate it
as a candidate AGB star, with a dust mass loss rate de-
rived from IR colours of 10−8.17 – 10−7.25 M⊙yr−1, depend-
ing on the specific colour. It is among the most luminous
AGB stars in the Magellanic Clouds, with only one object
in the LMC having similar luminosity, IRAS 04496−6958
(van Loon et al. 1998). Matsuura et al. (2005) suggest that
this is a post-AGB star, based on the presence of the 3.3-µm
PAH emission feature. Because of the presence of weak C2H2
absorption in the IRS spectrum, we classify it as C-AGB.
NGC 330 SW 515 (SMC IRS 239) is an irregular opti-
cal variable (Sebo & Wood 1994), with a possible 45-day
c
0000 RAS, MNRAS 000, 000–000
Spitzer-IRS point source classification in the SMC 33
orbital period but also variability on both shorter and
longer timescales (Schmidtke et al. 2008), and a possible
member of the cluster NGC 330. It features broad H α
emission (Meyssonnier & Azzopardi 1993; Oliveira et al.
2013), which is double peaked (Hummel et al. 1999), as
well as near-IR hydrogen emission (Tanab´e et al. 2013).
Martayan et al. (2007) classified it as a HeB[e] object. Mid-
IR excess emission was detected with the Infrared Space Ob-
servatory (ISO) by Kuˇcinskas et al. (2000) and with Spitzer
by Bolatto et al. (2007). The Spitzer IRS spectrum was first
published by Oliveira et al. (2013), who recognised it as a
young star but with no trace of H2O or CO2ices.
Lin 517 (SMC IRS 240) is also known as [BSS2007 282]
and LHA 115-N 86. It appears in earlier lists of H αsources
and possible PNe, e.g. Henize (1956), Lindsay (1961).
Kamath et al. (2014) find that it may be a hot post-AGB
star. We classify this object as YSO-4.
[MA93] 1771 (SMC IRS 241) is also 2MASS
J01134116−7250499 and SSTISAGEMA
J011341.20−725049.8. It is a known H αsource
(Meyssonnier & Azzopardi 1993), who believe it to be
the red component of a 2 arcsec pair, and possibly related
to Lin 497. Indeed, the MCPS survey (Zaritsky et al. 2002)
shows three potential counterparts within 3 arcsec of the
SAGE-SMC position (Gordon et al. 2011). This very red
source is also detected within 3 arcsec by Herschel in the
Herschel Inventory of the Agents of Galaxy Evolution
survey (HERITAGE; Meixner et al. 2013) at 100, 160 and
250 µm. Kamath et al. (2014) find that this object may be
a hot post-AGB star.
2MASS J00540342−7319384 (SMC IRS 242) is ob ject 18
in the spectral catalogue by Oliveira et al. (2013). It is
identified as a YSO candidate based on MIPS SED data
(van Loon et al. 2008) and the IRS spectrum (this work;
Oliveira et al. 2011).
2MASS J01054645−7147053 (SMC IRS 243). Initially pro-
posed as a YSO (Bolatto et al. 2007), this object has since
been classified as a carbon-rich proto-planetary nebula by
Volk et al. (2011), who point out the strong mid-IR emission
features usually attributed to PAHs, and a hint of a weak 21-
µm emission feature of which the carrier remains unknown.
They derived a luminosity of 4660 ±510 L⊙and birth mass
of only 1.00+0.12
−0.04 M⊙– which seems low for the carbon en-
richment. Kamath et al. (2014) derive L= 4106 L⊙and,
based on the presence of atomic emission lines and a UV
continuum, conclude that this is a hot post-AGB star.
2MASS J00540236−7321182 (SMC IRS 244) is ob ject 17
in the spectral catalogue by Oliveira et al. (2013). It is
identified as a YSO candidate based on MIPS SED data
(van Loon et al. 2008) and the IRS spectrum (this work;
Oliveira et al. 2011).
OGLE SMC-SC10 107856 (SMC IRS 245) is a (strong) can-
didate R CrB type star (Tisserand et al. 2009), experienc-
ing erratic, sudden obscuration events by circumstellar car-
bonaceous dust clouds. Polsdofer et al. (2015) and Riebel et
al. (in prep.) list it as an infrared variable. It has a relatively
cool atmosphere, ∼5000 K compared to most R CrB stars.
IRAS 00516−7259 (SMC IRS 246) is entry 16 in the spec-
tral catalogue of YSO candidates by Oliveira et al. (2013).
IRAS 00509−7342 (SMC IRS 247) is entry 15 in the spec-
tral catalogue of YSO candidates by Oliveira et al. (2013),
who also report extended radio continuum emission at 1.42,
2.37, 4.80 and 8.64 GHz at the same position. Kamath et al.
(2014) confirm the YSO nature of this source.
2MASS J00505814−7307567 (SMC IRS 248) is entry
14 in the catalogue by Oliveira et al. (2013). It is also
known as an H αemitter (Meyssonnier & Azzopardi 1993).
Kamath et al. (2014) confirm the YSO nature of this source.
2MASS J00504326−7246558 (SMC IRS 249) is entry
13 in the spectral catalogue of YSO candidates by
Oliveira et al. (2013), while it is also know as an H αemit-
ter (Meyssonnier & Azzopardi 1993). It appears to be part
of a star cluster (Bica & Schmitt 1995; Chiosi et al. 2006).
Kamath et al. (2014) confirm the YSO nature of this source.
2MASS J00504042−7320369 (SMC IRS 250) is entry 12 in
the spectral atlas by Oliveira et al. (2013).
2MASS J00494469−7324331 (SMC IRS 251) is entry 11 in
the spectral atlas by Oliveira et al. (2013).
SMP SMC 21 (SMC IRS 252) is a well known SMC plan-
etary nebula first identified by (Lindsay 1961). Our classi-
fication as an O-rich PN is consistent with the abundance
analyses available in the literature (i.e. Leisy & Dennefeld
1996).
Massey SMC 60447 (SMC IRS 253) was first catalogued
by Basinski et al. (1967) where it is ob ject 353 in their Ta-
ble V. The object was then classified as a red supergiant
star in Sanduleak (1989) where it is object 276; the po-
sitions are slightly different in these two papers but it is
clearly the same object. The spectral type is given as K2I in
Massey (2002). This is all consistent with our classification
of RSG. The source is also known to vary in the infrared
(Polsdofer et al. 2015).
PMMR 145 (SMC IRS 254) was first noted by Prevot et al.
(1983), as a red supergiant of spectral type K5 to K8. The
object is also discussed by Elias et al. (1985). An abundance
analysis was carried out by Hill (1997), who gives parame-
ters Teff = 4300 K, log g= +0.3, and [M/H] = −0.6 along
with a radial velocity of 160.6 km s−1. Analysis of the CNO
abundances by Hill et al. (1997) yields a C/O ratio of 0.3.
All of these observations are consistent with our classifica-
tion of the object as RSG.
PMMR 141 (SMC IRS 255) Prevot et al. (1983) catalogue
this star as a late-type supergiant. The spectral type is given
as K7–M0I by Massey & Olsen (2003). All the references to
this object in the literature are consistent with our classifi-
cation of the object as RSG.
PMMR 132 (SMC IRS 256) was catalogued as a late-
type supergiant in the SMC by Prevot et al. (1983) based
upon objective prism observations. Photometry is given in
Elias et al. (1985). We classify it as RSG.
LHA 115-S 38 (SMC IRS 257) was identified as an emission
line object by Henize (1956). It was then also catalogued by
Lindsay (1961) as Lin 418. The spectral type is given as be-
tween A3 and F0 in Evans et al. (2004b, object 1804). The
star is also discussed by Raimondo et al. (2005) as a likely
carbon-rich object based on the J−Kcolour. Kamath et al.
(2014) identify this object as a post-AGB candidate (# 38
in their Q1 list), showing a slow brightening in the optical
combined with a long period of ∼900 days, possibly due to
changes in the dust obscuration or the accretion rate. The
IRS spectrum, reveals its O-rich nature and we are able clas-
sify this object as O-PAGB.
RAW 594 (SMC IRS 258) was identified as a probable
carbon-rich variable star by Rebeirot et al. (1993) based on
c
0000 RAS, MNRAS 000, 000–000
34 Paul M. E. Ruffle et al.
its near-infrared colours. There are 4 other papers in the
literature concerning the variability or SED properties of
the object, which is a semi-regular pulsator from the OGLE
survey. Our IRS spectrum classification confirms the carbon-
rich nature and we classify it as C-AGB.
2MASS J00444463−7314076 (SMC IRS 259). Nothing spe-
cific is known about this object, except that it is an infrared
variable (Polsdofer et al. 2015).
SSTISAGEMA J005419.21−722909.7 (SMC IRS 260) was
identified based on its IRAC colours as a YSO candidate
by Bolatto et al. (2007), as YSO candidate 139 in their list
([BSS2007] 139), and as such included in the YSO sample to
be observed with Spitzer-IRS by Oliveira et al. (2013, entry
#19). However, these authors find that this object is not
a YSO, but rather a D-type symbiotic star, consisting of
an AGB star and white dwarf, with mass transfer between
them. There is also a nearby blue star (about 2.5 arcsec
away from the symbiotic binary) contributing a continuum
to the spectrum that cannot be separated out (Oliveira et al.
2013).
2MASS J00432649−7326433 (SMC IRS 261) is a semi-
regular variable carbon star (Raimondo et al. 2005;
Soszy´nski et al. 2011). It is also in the Polsdofer et al. (2015)
list of infrared variables.
Lin 250 (SMC IRS 262), also known as LHA 115-S 18, is
a well-known B[e] supergiant (see e.g. Clark et al. 2013 and
references therein for a comprehensive view of this system).
It is an infrared variable (Polsdofer et al. 2015, Riebel et
al. in prep.).
IRAS 00471−7352 (SMC IRS 263), is known to be a long
period variable (Groenewegen 2004; Raimondo et al.
2005; Soszy´nski et al. 2011), carbon-rich in nature
(Raimondo et al. 2005). It is also an infrared variable
(Polsdofer et al. 2015).
SSTISAGEMA J004901.61−731109.5 (SMC IRS 264) is en-
try 10 in the Spitzer -IRS spectral atlas of YSO candidates
by Oliveira et al. (2013).
LHA 115-N 31 (SMC IRS 265), also known as Lin 120, is an
emission line star (Henize 1956; Meyssonnier & Azzopardi
1993). It is classified as a candidate YSO by Bolatto et al.
(2007), while Charmandaris et al. (2008) included it in their
sample of candidate compact Hii regions, as object #5, and
remark that the IRAC colours set it apart from class I and
class II YSOs. LHA 115-N 31 is also entry 9 in the Spitzer -
IRS spectral atlas of YSO candidates by Oliveira et al.
(2013).
Lin 60 (SMC IRS 266) is also known as LHA 115-N 10 (see
e.g. Meyssonnier & Azzopardi 1993). It was one of the sam-
ple with MIPS spectra obtained by van Loon et al. (2010),
and Oliveira et al. (2013) examined it as a bright YSO as
well. Its spectrum has clear CO2ice absorption at 15 µm.
It appears in older lists, such as Henize (1956) and Lindsay
(1961).
S3MC J004825.83−730557.29 (SMC IRS 267) is found in
a complex region, and is therefore not identified as a point
source by the SAGE-SMC team (Gordon et al. 2011), but its
flux levels were extracted by the S3MC team (Bolatto et al.
2007), who also classify it as a candidate YSO. This is en-
try #8 in the IRS spectral catalogue of YSO candidates
by Oliveira et al. (2013), who report detections of CO2ice
and PAHs. Kamath et al. (2014) offer an alternative view by
classifying this as a candidate PN. We classify this object as
YSO-1.
2MASS J00444111−7321361 (SMC IRS 268) is a small-
amplitude semi-regular variable star, with P≈98
days (Soszy´nski et al. 2011), later refined to 96.338 days
(Kamath et al. 2014). While it was selected as a candi-
date YSO on the basis of mid-IR photometry (Bolatto et al.
2007), it has subsequently been shown to be a post-AGB ob-
ject on the basis of its 21-µm emission feature (Volk et al.
2011). The post-AGB nature was confirmed by the measure-
ment of extreme s-process elemental enhancements, its car-
bon enrichment (with C/O >1), and iron depletion, but not
the otherwise expected lead overabundance; a birth mass of
∼1.3 M⊙was inferred (De Smedt et al. 2012, 2014).
2MASS J00465185−7315248 (SMC IRS 269) appears to
be slightly extended at IRAC wavelengths, and is there-
fore not identified as a point source by the SAGE-SMC
team (Gordon et al. 2011). The S3MC team (Bolatto et al.
2007) was able to fit a point source and extract the flux
levesl. They also classify it as a candidate YSO. This is en-
try #7 in the IRS spectral catalogue of YSO candidates by
Oliveira et al. (2013), who report the presence of PAH emis-
sion.
S3MC J004624.46−732207.30 (SMC IRS 270) is a YSO
candidate (Bolatto et al. 2007, #43), observed with MIPS
SED (van Loon et al. 2010, #3) and IRS (Oliveira et al.
2013, #6).
SSTISAGEMA J004547.53−732142.1 (SMC IRS 271) is en-
try 5 in the IRS spectral catalogue by Oliveira et al. (2013).
It is an infrared variable (Polsdofer et al. 2015).
2MASS J00452129−7312185 (SMC IRS 272) is entry 4
in the IRS spectral catalogue by Oliveira et al. (2013).
It also appears in the emission-line star catalogue by
Meyssonnier & Azzopardi (1993).
IRAS 00429−7313 (SMC IRS 273), also known as LI-
SMC 25, was originally thought of as an AGB star can-
didate, based on its IRAS detection (Loup et al. 1997).
More recently, it was recognized as an early-type YSO can-
didate, and it is included in the spectral catalogues by
van Loon et al. (2010, #1; who also provide a short liter-
ature review on this source) and Oliveira et al. (2013, #2).
Kamath et al. (2014) also list it as YSO candidate, showing
optical variability in the form of Cepheid-like small oscilla-
tions, with a period of 22.5 days.
LHA 115-N 8 (SMC IRS 274), also known as Lin 41, is
entry #1 in the IRS spectral catalogue of YSO candidates
by Oliveira et al. (2013). It is also known as an emission-line
star (Meyssonnier & Azzopardi 1993).
2MASS J01061966−7155592 (SMC IRS 275) is catalogued
as a YSO candidate by Bolatto et al. (2007, entry #257).
Based on its UV continuum and emission-line characteris-
tics, Kamath et al. (2014) also list this as a YSO candidate.
2MASS J01052863−7159426 (SMC IRS 276) is catalogued
as a YSO candidate by Bolatto et al. (2007, entry #251).
Based on its UV continuum and emission-line characteris-
tics, Kamath et al. (2014) also list this as a YSO candidate.
HV 12956 (SMC IRS 277) is a luminous (Mbol ∼ −6.5
mag), Mira-type variable with a period of 518 days
(Catchpole & Feast 1981; Wood et al. 1983; Soszy´nski et al.
2011; Yang & Jiang 2012). Polsdofer et al. (2015)
also list it as an infrared variable. This M5e-type
AGB star was identified with the mid-IR source
c
0000 RAS, MNRAS 000, 000–000
Spitzer-IRS point source classification in the SMC 35
IRAS 01074−7140 (Whitelock et al. 1989; Zijlstra et al.
1996; Groenewegen & Blommaert 1998; van Loon et al.
1998), and the mid-IR spectrum obtained with the ISO
satellite was analysed by Groenewegen et al. (2000). De-
spite being one of the better candidates in the SMC for
circumstellar maser emission, none was detected in deep
searches (van Loon et al. 2001). The star was found to be
lithium-rich, probably as a result of nuclear processing at
the base of the convection zone (Smith et al. 1995). A 3–4
µm spectrum was presented in van Loon et al. (2008).
2MASS J01035898-7255327 (SMC IRS 278) is entry #238
in the YSO candidate list by Bolatto et al. (2007).
LHA 115-N 61 (SMC IRS 279), also known as Lin 321; IRAS
00557-7248 and LI-SMC 121; this is a well-known emission
line nebula in the SMC first discovered by Henize (1956).
It was classified as a planetary nebula by Lindsay (1961)
based on a lack of detected optical continuum around Hα
and the presence of the [N i i] 6548/6584 forbidden lines.
For this reason the ob ject has sometimes been consid-
ered as a PN in the literature (i.e. Jacoby & De Marco
2002), although it was classified as an H i i region by
Henize & Westerlund (1963) and this was confirmed spec-
troscopically by Dufour & Killen (1977).
Lin 238 (SMC IRS 280) is a known emission-line star
(Lindsay 1961; Meyssonnier & Azzopardi 1993). More re-
cently it was included in the catalogue by Bolatto et al.
(2007, object 132) as a YSO candidate. It is an infrared
variable (Polsdofer et al. 2015).
HD 5980 (SMC IRS 281) is a famous 19-day eclips-
ing Wolf–Rayet (WR) binary (Breysacher & Perrier 1980;
Breysacher et al. 1982) with estimated masses of MA= 58–
79 M⊙and MB= 51–67 M⊙, respectively (Foellmi et al.
2008). Koenigsberger et al. (2014) report that the sys-
tem has in fact a third component, which is an O-
star in a eccentric orbit with a period of 96.56 days.
HD 5980 had already been recognised as peculiar well
over a century ago (Pickering & Fleming 1901), and
was identified as an emission-line star half a century
later (Henize 1956), with variable emission-line width
(Feast et al. 1960). It resides in the massive cluster
NGC 346, but its proper motion of (µα=−3.50 ±1.70 mas
yr−1,µδ=−2.40 ±1.60 mas yr−1; Hog et al. 1998) is
marginally significant. Component A, of WN type, un-
derwent Luminous Blue Variable (LBV)-type eruptions
in 1993 and 1994 (Barba et al. 1995, 1996; Cellone et al.
1996; Eenens & Morris 1996; Heydari-Malayeri et al. 1997;
Sterken & Breysacher 1997; Koenigsberger et al. 1995,
1996, 1998a,b; Moffat et al. 1998), creating a circumstel-
lar shell (Morris et al. 1996; Koenigsberger et al. 2000,
2001; Gonz´alez & Koenigsberger 2014; Dopita et al. 1994),
as well as showing longer term S Doradus-type variability
(Koenigsberger et al. 2010; Georgiev et al. 2011) and spec-
tral changes preceding the outburst (Koenigsberger et al.
1994). HD 5980 is a b right, variable X -ray source (Naz´e et al.
2004; Guerrero & Chu 2008) as a result of colliding
winds (Breysacher & Fran¸cois 2000; Koenigsberger 2004;
Koenigsberger et al. 2006; Koenigsberger & Moreno 2008);
polarimetric variability indicates complex structure and/or
a neutron star companion (Villar-Sbaffi et al. 2003). In-
deed, the supernova remnant SNR 0057−7226 lies in the
direction towards HD 5980 (Hoopes et al. 2001; Naz´e et al.
2002; Vel´azquez et al. 2003). The binary was detected at
mid-IR wavelengths with ISO by Contursi et al. (2000);
the Spitzer mid-IR photometric properties were analysed
by Bonanos et al. (2010), who point out that this is the
only WR star (but not the only LBV) in the SMC with
a detection at 24 µm. Being such bright, early-type, line-
broadened star, HD 5980 has been u sed ext ensively as
a background probe for interstellar medium studies (de-
spite its low E(B−V) = 0.05 mag – Schmutz & Vacca
1991) – e.g., polarization (Schmidt 1970; Mathewson & Ford
1970); UV (de Boer & Savage 1980; Savage & de Boer
1981; Fitzpatrick & Savage 1983, 1985; Sembach & Savage
1992) including detection of H2(Richter et al. 1998;
Shull et al. 2000) – see also Cohen (1984); Songaila et al.
(1986); Sembach et al. (1993); Lipman & Pettini (1995) and
Hoopes et al. (2002). Polsdofer et al. (2015) list it as an in-
frared variable.
HD 6884 (SMC IRS 282) (or R 40) is a luminous blue su-
pergiant (Feast et al. 1960) of type B9 Iae (Garmany et al.
1987; B8 Ia based on UV – Smith Neubig & Bruhweiler
1997) displaying H αline emission (LHA 115-S 52; Henize
1956), with confirmed membership of the SMC based on a
radial velocity of 170 km s−1(Buscombe & Kennedy 1962).
It is the visually brightest B star (Stahl et al. 1985) and
the first recognised LBV in the SMC (Szeifert et al. 1993),
explaining the later spectral type of A2 determined by
(Lennon 1997) and th e S Dor-type variability (Sterken et al.
1998). Early optical photometry was presented by Dachs
(1970), Osmer (1973), Ardeberg & Maurice (1977) and
van Genderen et al. (1982); a K-band spectrum was pre-
sented by Oksala et al. (2013). Not surprisingly, it has been
used extensively for studies of the interstellar medium (e.g.,
Cohen 1984; Songaila et al. 1986); the 4430-˚
A diffuse in-
terstellar band was detected in its spectrum by Hutchings
(1966), and the degree of polarization was measured by
Mathewson & Ford (1970). Bonanos et al. (2010) detected
mid-IR excess emission on the basis of Spitzer photometry.
It is in the Polsdofer et al. (2015) list of infrared variables.
2MASS J00531330−7312176 (SMC IRS 283) is entry
#131 in the YSO candidate list by Bolatto et al. (2007).
The source is possibly also detected in the far-infrared
(Wilke et al. 2003), as [WSH2003] b-63, although the co-
ordinates are very coarse at these wavelengths. Within 10
arcsec, another far-infrared detection with Herschel has
also been reported, again with rather imprecise coordinates
(Meixner et al. 2013).
2MASS J00531330−7312176 (SMC IRS 284) is entry #129
in the YSO candidate list by Bolatto et al. (2007).
2MASS J00505425−7324170 (SMC IRS 286). is YSO can-
didate 112 in the catalogue by Bolatto et al. (2007).
LHA 115-N 32 (SMC IRS 287) LHA 115-N 32 is a well
known source, with more than 20 references, starting with
Henize (1956) and Lindsay (1961). It has been charac-
terized more as an H ii region than a PN (most recently
by Charmandaris et al. 2008). We classify the spectrum as
YSO-3, but remark that it is due from a source located
within an H i i region.
2MASS J00484901−7311226 (SMC IRS 288) is entry #83
in the list of YSO candidates by Bolatto et al. (2007). In
contrast, Kamath et al. (2014) catalogue this object as a
hot post-AGB candidate. We classify it as YSO-3.
2MASS J00465576−7331584 (SMC IRS 289) is entry #47
in the list of YSO candidates by Bolatto et al. (2007).
c
0000 RAS, MNRAS 000, 000–000
36 Paul M. E. Ruffle et al.
Kamath et al. (2014) also list this object as a candidate
YSO.
2MASS J00454296−7317263 (SMC IRS 290) is entry #27
in the list of YSO candidates by Bolatto et al. (2007).
IRAS 01042−7215 (SMC IRS 291). Wilke et al. (2003) de-
termined the 25- and 60-µm flux densities from high reso-
lution IRAS maps (source b-97), to be F25 = 0.6±0.1 and
F60 = 8.4±0.3 Jy (cf. Schwering & Israel 1989); they did not
detect the source in their ISO-PHOT maps at a wavelength
of 170 µm. A far-IR spectrum obtained with the Spitzer SED
mode was presented by van Loon et al. (2010). The near-
IR counterpart was found by Groenewegen & Blommaert
(1998). While Groenewegen et al. (2000) modelled the ISO
mid-IR data as if it were a mass-losing cool oxygen-rich
AGB star, van Loon et al. (2008) classified it as a candidate
YSO on the basis of a 3–4-µm spectrum displaying water ice
absorption and hydrogen recombination emission. Indeed,
Oliveira et al. (2011) detected (weak) CO2ice absorption
in the Spitzer IRS spectrum confirming the YSO nature of
this object; CO ice was not detected in their groundbased
M-band spectrum. Oliveira et al. (2013) also presented an
optical spectrum showing just broad H αemission, as well
as new near-IR photometry (J KSL′). Polsdofer et al. (2015)
list it as an infrared variable.
Lin 49 (SMC IRS 292) has been known as an emission line
source and/or a PN (Lindsay 1961; Henize & Westerlund
1963; Dopita et al. 1985; Meyssonnier & Azzopardi 1993;
Morgan 1995). While Bolatto et al. (2007) included it in
their YSO candidate list (#7), the IRS spectrum clearly
shows that this is a C-PN, and a fullerene source (this work;
Sloan et al. 2014).
2MASS J00431490−7300426 (SMC IRS 294) is entry #4 in
the list of YSO candidates by Bolatto et al. (2007).
NGC 330 BAL 555 (SMC IRS 296) is another member of
NGC 330, and is known to be a long period semi-regular vari-
able from OGLE observations (Soszy´nski et al. 2011). The
object appears to have first been catalogued as a member of
NGC 330 by Balona (1992) where it is object 555 in Table
2. Kamath et al. (2014) list it as a carbon star, consistent
with our classification of this object as C-AGB.
2MASS J01065966−7250430 (SMC IRS 298) is an emission-
line star (Meyssonnier & Azzopardi 1993), listed as a can-
didate PN by Kamath et al. (2014). van Loon et al. (2010)
list it as a YSO (entry 11), and the IRS spectrum confirms
the YSO nature of this object (Oliveira et al. 2013, #30).
We classify it as YSO-3.
2MASS J01053088−7155209 (SMC IRS 299) is entry 29
in the IRS spectral catalogue of YSO candidates by
Oliveira et al. (2013).
2MASS J01050732−7159427 (SMC IRS 300) is entry 8 in
the study by van Loon et al. (2010), who list it as a YSO,
and provide some further references. Its YSO nature is con-
firmed by its IRS spectrum (Oliveira et al. 2013, #28).
S3MC J010306.13−720343.95 (SMC IRS 301) is entry 228
in the YSO candidate list by Bolatto et al. (2007), and its
YSO nature is confirmed by its IRS spectrum (Oliveira et al.
2013, #27).
S3MC J010248.54−715317.98 (SMC IRS 302) is an mid-
infrared point source (also detected by the SAGE team
as SSTISAGEMA J010248.56−715318.0) part of star form-
ing region A8 discovered by (Livanou et al. 2007), which is
about 240 pc in size. Region A8 contains several H i i re-
gions, and S3MC J010248.54−715317.98 is located inside
one of these H i i regions, namely DEM S 117b, also known as
LHA 115-N 77A (Bica & Schmitt 1995), which has a size of
0.55 arcmin. The IRS spectrum therefore shows many emis-
sion lines due to the H ii region. We conclude that the point
source is an YSO-3 object located within an H ii region (see
also Oliveira et al. 2013, #26).
S3MC J010131.69−715040.30 (SMC IRS 303) is entry
25 in the IRS spectral catalogue of YSO candidates by
Oliveira et al. (2013), and entry 210 in the list of YSO can-
didates of Bolatto et al. (2007).
SSTISAGEMA J010022.34-720957.8 (SMC IRS 304) is en-
try 24 in the IRS spectral catalogue of YSO candidates by
Oliveira et al. (2013), and it is also entry 60 in the list of
YSOs in N66 compiled by Simon et al. (2007), who derive
L= 2910 L⊙and M= 8 M⊙for this source. It is also known
to vary in the infrared (Polsdofer et al. 2015, Riebel et al. in
prep.).
IRAS 00563−7220 (SMC IRS 305) is entry 23 in the
IRS spectral catalogue of YSO candidates by Oliveira et al.
(2013). It is also #174 in the YSO candidate list published
by Bolatto et al. (2007).
IRAS 005627255 (SMC IRS 306) is entry 22 in the IRS spec-
tral catalogue of YSO candidates by Oliveira et al. (2013).
It is also #171 in the YSO candidate list published by
Bolatto et al. (2007).
2MASS J00560662−7247225 (SMC IRS 307) is reported to
be an emission-line star (Meyssonnier & Azzopardi 1993),
perhaps consisting of multiple components. It is also en-
try 21 in the IRS spectral catalogue of YSO candidates by
Oliveira et al. (2013). Bolatto et al. (2007) list it as #146
in their list of YSO candidates, and it is also included as
a YSO candidate in the work by Kamath et al. (2014). We
classify it as YSO-1.
HV 11464 (SMC IRS 309) is first classified as M0 I by
Prevot et al. (1983) and Elias et al. (1985); SMC member-
ship was confirmed based on the heliocentric radial veloc-
ity of vhel = 189 km s−1(Maurice et al. 1987); however
the spectral type was revised to K0 I and the radial ve-
locity to 182 km s−1by Massey & Olsen (2003), who also
determined a bolometric luminosity of Mbol =−8.0 mag.
Yang & Jiang (2012) determined a long secondary period of
1500–1600 days. The Spitzer mid-IR photometry was anal-
ysed by Bonanos et al. (2010). It straddles the boundary
between the RSG and AGB classification, and because of
its Mbol value we classify it as O-AGB.
IRAS 00436−7321 (SMC IRS 310) is in a complex field. The
source is also an emission-line star and listed as entry 108
in the H αsurvey by Meyssonnier & Azzopardi (1993). The
IRAS name is cross-identified with this Spitzer source, as
it is the only source with a MIPS-[24] flux level comparable
to the IRAS -[25] flux within the error box of the IRAS -[25]
position (no detection at IRAS -[12]). Keller et al. (in prep.)
believe this source to be a PN, however we classify it as HII.
NGC 330 ARP 41 (SMC IRS 311), a member of the NGC
330 cluster, has been known to be a late-type supergiant
since the 1970’s. The star was first observed by Arp (1959)
as object 41 in his list. The spectral type was determined as
G6Ib by Feast (1979). Our classification of this ob ject as a
red supergiant is (marginally) consistent with this spectral
type.
c
0000 RAS, MNRAS 000, 000–000
Spitzer-IRS point source classification in the SMC 37
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