The Leo IV Dwarf Spheroidal Galaxy: Color-Magnitude Diagram and Pulsating Stars

Abstract

We present the first V, B – V color-magnitude diagram of the Leo IV dwarf spheroidal galaxy, a faint Milky Way satellite recently discovered by the Sloan Digital Sky Survey. We have obtained B, V time-series photometry reaching about half a magnitude below the Leo IV turnoff, which we detect at V = 24.7 mag, and have performed the first study of the variable star population. We have identified three RR Lyrae stars (all fundamental-mode pulsators, RRab) and one SX Phoenicis variable in the galaxy. In the period-amplitude diagram the Leo IV RR Lyrae stars are located close to the loci of Oosterhoff type I systems and the evolved fundamental-mode RR Lyrae stars in the Galactic globular cluster M3. However, their mean pulsation period, Pab = 0.655 days, would suggest an Oosterhoff type II classification for this galaxy. The RR Lyrae stars trace very well the galaxy's horizontal branch, setting its average magnitude at V
RR = 21.48 ± 0.03 mag (standard deviation of the mean). This leads to a distance modulus of μ0 = 20.94 ± 0.07 mag, corresponding to a distance of 154 ± 5 kpc, by adopting for the Leo IV dSph a reddening E(B – V) = 0.04 ± 0.01 mag and a metallicity of [Fe/H] = –2.31 ± 0.10.

Full text

The Astrophysical Journal, 699:L125–L129, 2009 July 10 doi:10.1088/0004-637X/699/2/L125
C
2009. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
THE LEO IV DWARF SPHEROIDAL GALAXY: COLOR–MAGNITUDE DIAGRAM AND PULSATING STARS∗
Maria Ida Moretti1, Massimo Dall’Ora2, Vincenzo Ripepi2, Gisella Clementini3, Luca Di Fabrizio4,
Horace A. Smith5, Nathan De Lee6, Charles Kuehn5,M
´
arcio Catelan7,10,11 , Marcella Marconi2, Ilaria Musella2,
Timothy C. Beers5,8, and Karen Kinemuchi6,9
1Dipartimento di Astronomia, Universit`
a di Bologna, Bologna, Italy; mariaida.moretti@studio.unibo.it
2INAF, Osservatorio Astronomico di Capodimonte, Napoli, Italy; dallora@na.astro.it,ripepi@na.astro.it
3INAF, Osservatorio Astronomico di Bologna, Bologna, Italy; gisella.clementini@oabo.inaf.it
4INAF, Centro Galileo Galilei & Telescopio Nazionale Galileo, S. Cruz de La Palma, Spain; difabrizio@tng.iac.es
5Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824-2320, USA; smith@pa.msu.edu,kuehncha@pa.msu.edu,
beers@pa.msu.edu
6Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611-2055, USA; ndelee@astro.ufl.edu
7Pontificia Universidad Cat´
olica de Chile, Departamento de Astronom´
ıa y Astrof´
ısica, Santiago, Chile; mcatelan@astro.puc.cl
8Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824, USA
9Universidad de Concepci´
on, Departamento de F´
ısica, Concepci´
on, Chile, kkinemuchi@astro-udec.cl
Received 2009 March 20; accepted 2009 May 29; published 2009 June 22
ABSTRACT
We present the first V,B −Vcolor–magnitude diagram of the Leo IV dwarf spheroidal galaxy, a faint Milky
Way satellite recently discovered by the Sloan Digital Sky Survey. We have obtained B,V time-series photometry
reaching about half a magnitude below the Leo IV turnoff, which we detect at V=24.7 mag, and have performed the
first study of the variable star population. We have identified three RR Lyrae stars (all fundamental-mode pulsators,
RRab) and one SX Phoenicis variable in the galaxy. In the period–amplitude diagram the Leo IV RR Lyrae stars
are located close to the loci of Oosterhoff type I systems and the evolved fundamental-mode RR Lyrae stars in
the Galactic globular cluster M3. However, their mean pulsation period, Pab=0.655 days, would suggest
an Oosterhoff type II classification for this galaxy. The RR Lyrae stars trace very well the galaxy’s horizontal
branch, setting its average magnitude at VRR=21.48 ±0.03 mag (standard deviation of the mean). This leads
to a distance modulus of μ0=20.94 ±0.07 mag, corresponding to a distance of 154 ±5 kpc, by adopting
for the Leo IV dSph a reddening E(B−V)=0.04 ±0.01 mag and a metallicity of [Fe/H] =−2.31 ±0.10.
Key words: galaxies: dwarf – galaxies: individual (Leo IV) – stars: distances – stars: variables: other – techniques:
photometric
1. INTRODUCTION
Dwarf Spheroidal (dSph) galaxies (Mateo 1998) provide im-
portant constraints on Λcold dark matter (ΛCDM) theories of
galaxy formation, which predict that several hundred small dark
halo satellites should surround the halos of large galaxies like
the Milky Way (MW) and M31 (Klypin et al. 1999; Moore et al.
1999), and that dSphs are the best candidates for the “building
blocks” from which the MW and M31 were assembled (Searle
&Zinn1978). Indeed, there is a sizeable discrepancy between
ΛCDM theory and observations, known as the “missing satellite
problem” (Kauffmann et al. 1993; Tollerud et al. 2008), since the
number of satellites predicted by theory is much higher than the
number of dSphs actually observed surrounding the MW. Solv-
ing the “missing satellite problem” would require the discovery
of many new dSph satellites of our Galaxy (e.g., Walsh et al.
2009).
The dSph galaxies surrounding the MW can be divided into
two groups: “bright” dSphs, mainly discovered before 2005, and
“faint” dSphs, discovered in the last couple of years primarily
from the analysis of imaging obtained by the Sloan Digital Sky
∗Based on data collected at the 2.5 m Isaac Newton Telescope, La Palma,
Canary Island, Spain, at the 4.2 m William Herschel Telescope, Roche de los
Muchachos, Canary Islands, Spain, and at the 4.1 m Southern Astrophysical
Research Telescope, Cerro Pach´
on, Chile.
10 On sabbatical leave at Michigan State University, Department of Physics
and Astronomy, 3215 Biomedical and Physical Sciences Bldg., East Lansing,
MI 48824, USA.
11 John Simon Guggenheim Memorial Foundation Fellow.
Survey (SDSS; York et al. 2000). Bright and faint dSphs lie in
two separate regions in the absolute magnitude versus half-light
radius plane (see Figure 8 of Belokurov et al. 2007, hereafter
B07).
The bright dSphs include 10 systems (Draco, Ursa Minor, For-
nax, Carina, Sculptor, Leo I, Leo II, Sextans, Sagittarius, and
Canis Major; Mateo 1998; Ibata et al. 1995; Irwin & Hatzidim-
itriou 1995; Martin et al. 2004). These galaxies generally are
found to contain stars exhibiting different chemical composi-
tions than the stars in the Galactic halo (see Helmi et al. 2006,
and references therein). Furthermore, they generally host RR
Lyrae stars with pulsation properties that differ from the proper-
ties of the variables in the Galactic globular clusters (GCs), be-
ing “Oosterhoff-intermediate” (Oosterhoff 1939; Catelan 2009,
and references therein). These two properties suggest that it
is unlikely that the halo of the MW was formed from objects
with properties similar to the bright dSphs that are observed
today.
Since 2005, 15 new faint (effective surface brightnesses
μV28 arcsec−2) dSph satellites of the MW have been
discovered, primarily from SDSS imaging: Willman I, Ursa
Major I, Ursa Major II, Bootes I, Coma Berenices (Coma),
Segue I, Canes Venatici I (CVn I), Canes Venatici II (CVn II),
Leo IV, Hercules, Leo T, Bootes II, Leo V, Bootes III, and
Segue II (Willman et al. 2005a,2005b; Zucker et al. 2006a,
2006b; Grillmair 2006,2009; Belokurov et al. 2006,2007,
2008,2009; Irwin et al. 2007; Walsh et al. 2007). These faint
galaxies have high mass-to-light ratios and (often) distorted
morphologies, probably due to tidal interactions with the MW.
L125

L126 MORETTI ET AL. Vol. 699
They all host an ancient stellar population with chemical
properties similar to that of external Galactic halo stars (Simon
& Geha 2007; Kirby et al. 2008; Frebel et al. 2009). Several of
the faint dSphs have mean metallicities as low or lower than the
most metal-poor GCs and, generally, much lower than those of
the bright dSphs.
Galactic GCs that contain significant numbers of RR Lyrae
stars have fundamental-mode (RRab) pulsators with mean
period (Pab) either around 0.55 days or around 0.65 days, and
separate into the so-called Oosterhoff I (Oo I) and Oosterhoff II
(Oo II) types (Oosterhoff 1939). Extragalactic GCs and field RR
Lyrae stars in the bright dSph galaxies generally have, instead,
Pabintermediate between the two types (Catelan 2009 and
references therein). Four of the faint dSphs have been searched
for variable stars so far (namely, Bootes I, Dall’Ora et al. 2006,
Siegel 2006; CVn I, Kuehn et al. 2008; CVn II, Greco et al.
2008; and Coma, Musella et al. 2009) and, with the exception
of CVn I, were found to contain RR Lyrae stars with properties
resembling those of the MW Oo II GCs.
All of the above characteristics suggest that a much larger
population of objects similar to the presently observed faint
dSphs may have been the “building blocks” of the halos of
large galaxies such as the MW. The association is particularly
clear with the outer halo of the MW, which Carollo et al.
(2007) have demonstrated to exhibit a peak metallicity of [Fe/
H] =−2.2, substantially lower than the inner halo (with a peak
at [Fe/H] =−1.6), and which is the dominant population at
Galactocentric distances beyond 15–20 kpc.
The Leo IV galaxy (R.A. =11h32m57s, decl. =−00◦3200,
J2000.0; l=265.
◦4, b=56.
◦5) is one of the newly discovered
SDSS dSphs, with absolute magnitude MV=−5.1±0.6
mag (B07) and surface brightness μV=28.3 mag arcsec−2
(Simon & Geha 2007). It is a low-mass (M=(1.4 ±1.5) ×
106M; Simon & Geha 2007) system, with half-light radius
rh∼3.3 arcmin (B07). It is located at heliocentric distance
160+15
−14 kpc with a position angle of 355◦(B07). Its color–
magnitude diagram (CMD) is more complex than the CMDs
of other galaxies discovered by Belokurov et al., due to the
presence of an apparently “thick” red giant branch (RGB) and
a blue horizontal branch (HB). The RGB thickness suggests
the presence of stellar populations of different age/metallicity
(B07). There is no published CMD of Leo IV other than the i,
g−iCMD that reaches i∼22 mag obtained from the SDSS
discovery data, nor has a study of the variable stars in the
galaxy yet been performed. Simon & Geha (2007) obtained
spectra for 18 bright stars in Leo IV from which they derived
an average velocity dispersion of 3.3 ±1.7 km s−1and an
average metallicity [Fe/H]=−2.31 ±0.10 with a dispersion
σ[Fe/H] =0.15 dex, on the Zinn & West (1984) metallicity scale
(hereafter ZW84). Kirby et al. (2008), using Keck DEIMOS
spectroscopy coupled with spectral synthesis, measured the
metallicity of a subset of 12 stars extracted from the Simon
& Geha (2007) sample. They obtained an average metallicity
[Fe/H]=−2.58±0.08, with a dispersion σ[Fe/H] =0.75 dex
and individual metallicities as low as [Fe/H] ∼−3.0.
In this Letter, we present the first V,B−VCMD of the Leo IV
dSph, reaching a depth of V∼25.5 mag, sufficient to identify
the galaxy’s main-sequence turnoff at V∼24.7 mag. We carry
out a search for variable stars, and identify three fundamental-
mode RR Lyrae stars (RRab) and one SX Phoenicis (SX Phe)
variable. We obtained B,Vlight curves for each variable star
and use the average magnitude of the RR Lyrae stars to estimate
the distance to the galaxy.
2. OBSERVATIONS AND DATA REDUCTION
Time-series B,V,Iphotometry of the Leo IV dSph galaxy
was collected on 2007 April 20–23, with the Wide Field Cam-
era (WFC), the prime focus mosaic CCD camera of the 2.5 m
Isaac Newton Telescope (INT), on 2007 May 11–12, with the
Prime Focus Imaging Platform (PFPI) of the 4.2 m William
Hershel Telescope (WHT), and on 2007 March–May, with the
SOAR Optical Imager (SOI) of the 4.1 m SOuthern Astrophys-
ical Research telescope (SOAR). The fields of view (FOVs)
covered by the three instruments are: 5.24 ×5.24 arcmin2for
SOI at the SOAR telescope, 16.2 ×16.2 arcmin2for PFPI
at the WHT, and 33 ×33 arcmin2for WFC at the INT. We
needed two partially overlapping SOI fields to cover the galaxy,
while just one PFPI field was sufficient, and from the INT
data we could also infer additional information on stars out-
side the Leo IV half-light radius. We obtained a total number
of 37 B,42V, and 12 Iimages of the galaxy. In this Let-
ter, we present results from the analysis of the Band Vdata.
Images were reduced following standard procedures (bias sub-
traction and flat-field correction) with IRAF. The INT and WHT
data were corrected for linearity following recipes provided in
the telescope’s Web pages. We then performed PSF photom-
etry using the DAOPHOT/ALLSTAR/ALLFRAME packages
(Stetson 1987,1994). Typical internal errors of the B, V single-
frame photometry for stars at the HB level range from 0.02 to
0.03 mag for the INT and WHT data, and are of about 0.02 mag
for the SOAR data. The absolute photometric calibration was ob-
tained using observations of standard stars in the Landolt (1992)
fields SA 101, SA 107, SA 110, and PG1323, as extended by
P. B. Stetson,12 which were observed at the INT during the night
of 2007 April 22. Errors of the absolute photometric calibration
are σB=0.01 mag, σV=0.01 mag, respectively.
3. IDENTIFICATION OF THE VARIABLE STARS
Variable stars were identified using the Vand Btime-series
data separately. First we calculated the Fourier transforms (in the
Schwarzenberg-Czerny 1996 formulation) of the stars having
at least 12 measurements in each photometric band, then we
averaged these transforms to estimate the noise and calculated
the signal-to-noise ratios (S/Ns). Results from the Vand B
data sets were cross-correlated, and all stars with S/N>5in
both photometric bands were visually inspected, for a total of
about 2000 objects. We also checked whether some of the stars
in the Blue Straggler Stars (BSSs) region might be pulsating
variables of SX Phe type. The study of the light curves and
period derivation were carried out using the Graphical Analyzer
of Time Series package (GRaTiS; Clementini et al. 2000). We
confirmed the variability and obtained reliable periods and light
curves for 3 RR Lyrae stars, all fundamental-mode pulsators
(stars: V1, V2, and V3), and for one SX Phe variable (star
V4). The identification and properties of the confirmed variable
stars are summarized in Table 1, their light curves are shown
in Figure 1. The light-curve data of the variable stars and the
photometric data of the galaxy CMD are available on request
from the first author.
Stars V1, V2, and V4 lie inside the galaxy half-light radius,
while V3 lies outside, at about 12 arcmin from the Leo IV
center (see the lower panel of Figure 4). In the CMD, the SX
Phe star is located in the region of the BSSs, while all the RRab
stars (V3 included) fall near the galaxy’s HB. We checked the
12 See http://cadcwwwdao.nrc.ca/standards.

No. 2, 2009 THE LEO IV dSph GALAXY L127
Figure 1. V(left panels) and B(right panels) light curves of the variable stars discovered in the Leo IV dSph galaxy. Three upper rows: fundamental-mode RR Lyrae
stars; bottom row: SX Phe variable.
Tab l e 1
Identification and Properties of Variable Stars in the Leo IV dSph Galaxy
Name α(2000) δ(2000) Type P(days) Epoch (max) (−2450000) V(mag) B(mag) AV(mag) AB(mag) [Fe/H]ZW84 a
V1 11 32 59.2 −00 34 03.6 RRab 0.61895 4212.453 21.47 21.82 0.73 0.99 −2.11
V2 11 32 55.8 −00 33 29.4 RRab 0.7096 4214.543 21.46 21.86 0.64 0.76 −2.03
V3 11 33 36.6 −00 38 43.3 RRab 0.635 4212.453 21.52 21.81 0.65 0.82 ···
V4 11 32 45.4 −00 31 44.4 SX Phe 0.0994 4213.397 22.96 23.34 0.37 0.38 ···
Notes.
aThe metallicity of V1 was derived from the Fourier parameters of the V-band light curve. The metallicity of V2 is from Kirby et al. (2008).
position of V4 on the period–luminosity (PL) relation of the SX
Phe stars. Using the star’s period and the absolute magnitude
inferred from the apparent magnitude and the distance provided
by the RR Lyrae stars (see Section 4), we found that V4 lies
very close to the Poretti et al. (2008) PL relation for SX Phe
stars, thus confirming the classification as an SX Phe star.
So far, only four dSphs of Oosterhoff II type are known,
namely, Ursa Minor among the bright companions of the MW,
and Bootes I (Dall’Ora et al. 2006; Siegel 2006), CVn II (Greco
et al. 2008), and Coma (Musella et al. 2009), among the faint
SDSS dSphs. The average pulsation period of the Leo IV RRab
stars, Pab=0.655 days, would suggest that Leo IV too is
more similar to the Oosterhoff type II systems. However, in
the V-band period–amplitude diagram (see Figure 2)theLeoIV
RRab stars fall close to the locus of Oo I systems (from Clement
&Rowe2000), with V1 and V3 lying near the distribution of
the bona fide regular variables, and V2 lying close to the locus
of the well-evolved fundamental-mode RR Lyrae stars in the
Galactic GC M3 (from Cacciari et al. 2005). Nevertheless, V2
does not appear to be overluminous in the CMD, as would
be required if the star were evolved off the zero-age HB. The
ambiguous behavior and the small number of variable stars make
the conclusive assignment of an Oosterhoff type to the Leo IV
dSph rather difficult.
We used the parameters of the Fourier decomposition of the V-
band light curve, along with the Jurcsik & Kov´
acs (1996) method
Figure 2. V-band period–amplitude diagram of RR Lyrae stars in the Coma,
Bootes I, CVn II, and Leo IV dSphs. Variables with log P>−0.35 days
are RRab pulsators, those with log P<−0.35 days are first-overtone (RRc)
pulsators. Long-dashed and dot-dashed lines show the position of the Oo I and
Oo II Galactic GCs, according to Clement & Rowe (2000). Period–amplitude
distributions of the bona fide regular (solid curve) and well evolved (dashed
curve) RRab stars in M3, from Cacciari et al. (2005), are also shown for
comparison.

L128 MORETTI ET AL. Vol. 699
Figure 3. V,B−VCMD of the Leo IV dSph obtained by plotting stellar-like
objects located within the half-light radius of 3.3 arcmin. Variable stars V1, V2,
and V4 are marked by triangles, star V3 by a cross, and nonvariable HB stars
by (blue) filled circles. The solid line is the ridgeline of the Galactic GC M15.
The red and cyan dots are stars respectively within ±0.05 mag in B−Vand, for
V>23.5 mag, from ±0.05 and ±0.10 mag in B−Vfrom the ridgeline of M15.
The open circles mark member stars of the Leo IV dSph according to Simon &
Geha (2007) and Kirby et al. (2008).
for RRab stars, to estimate the metallicity on the ZW84 scale of
V1, the only variable of our RR Lyrae sample which satisfies the
Jurcsik & Kov´
acs (1996) regularity conditions. The metallicity
we derived for V1 is in good agreement with the spectroscopic
metallicity derived for another RR Lyrae star (variable V2) by
Kirby et al. (2008) (see the last column of Table 1).
4. THE CMD, STRUCTURE, AND DISTANCE OF LEO IV
Figure 3shows the V,B−VCMD of the Leo IV dSph
obtained by plotting all stellar-like objects located within
the half-light radius of 3.3 arcmin from the B07 center of
Leo IV. The selection between stars and galaxies, for magnitudes
brighter than V=22.5 mag, was done with the software Source
Extractor (SExtractor; Bertin & Arnouts 1996). Variable stars
are plotted in the CMD according to their intensity-averaged
magnitudes and colors (see Table 1), using filled triangles for
stars V1, V2, and V4, and a cross for V3. Although well
outside the Leo IV half-light radius, V3 appears to be perfectly
located on the galaxy’s HB, thus confirming its membership
to the galaxy. Nonvariable HB stars are marked by (blue)
filled circles. The CMD reaches V∼25.5 mag, and appears
to be heavily contaminated at every magnitude level by field
objects belonging to the MW. We used the mean ridgeline of
the Galactic GC M15 (from Durrell & Harris 1993; solid line)
properly shifted in magnitude and color, and selected as stars
most likely belonging to the Leo IV galaxy the sources lying
within ±0.05 mag from the ridgeline of M15 (red dots). To
allow for the larger photometric errors, for magnitudes fainter
than V=23.5 mag, we also considered as belonging to the
galaxy stars with B−Vcolor in the range from ±0.05 mag and
±0.10 mag from the ridgeline of M15 (cyan dots). The HB
Figure 4. Upper panel: map of sources in the FOV of the WHT observations,
which we consider to belong to the Leo IV galaxy according to the fit with
the M15 ridgeline, or with membership spectroscopically confirmed by Simon
&Geha(2007) (open circles). Symbols and color-coding are the same as in
Figure 3and, for nonvariable stars, the symbol sizes are proportional to the
star’s brightness. Lower panel: map of sources observed in the INT FOV which
lie within ±0.05 mag in B−V(for V>23.5 mag, within ±0.10 mag in B−V)
from the ridgeline of M15. The symbols and color-coding for the variable stars
are the same as in Figure 3. In both panels the large circle shows the region
corresponding to the half-light radius of Leo IV centered on the B07 coordinates
for the galaxy.
of Leo IV shows up quite clearly and, along with the galaxy’s
RGB, is well reproduced by the ridgeline of M15, implying
that Leo IV has an old and metal-poor stellar population with
metallicity comparable to that of M15 ([Fe/H] =−2.15 ±0.08,
on the ZW84 scale). We also note that, by adopting for M15 a
reddening value of E(B−V)=0.10 ±0.01 mag (Durrell &
Harris 1993), the color shift needed to match the HB and RGB

No. 2, 2009 THE LEO IV dSph GALAXY L129
of Leo IV implies for the galaxy a reddening of E(B−V)=
0.04 ±0.01 mag. For comparison, the reddening in the direction
of Leo IV obtained from the Schlegel et al. (1998) maps is
0.025 ±0.026 mag. The objects marked by the open circles are
stars within the Leo IV half-light radius, whose membership to
the galaxy was confirmed spectroscopically by Simon & Geha
(2007). They include the RR Lyrae star V2 and a number of
HB and RGB stars which fall very close to the M15 ridgeline,
thus supporting our identification of the Leo IV member
stars.
The upper panel of Figure 4shows a map of all sources
observed in the FOV of the WHT observations that we con-
sider to belong to the Leo IV galaxy, according to their position
with respect to the M15 ridgeline, or with membership spectro-
scopically confirmed by Simon & Geha (2007) (open circles).
Symbols and color-coding are the same as in Figure 3and, for
nonvariable stars, the symbol sizes are proportional to the star’s
brightness. The solid circle shows the region corresponding to
the half-light radius of Leo IV centered on the B07 coordinates
for the galaxy. The lower panel of Figure 4showsamapofthe
sources observed in the INT FOV which lie within ±0.05 mag
in B−V(for V>23.5 mag, within ±0.10 mag in B−V)from
the ridgeline of M15. An overdensity of objects rather extended
and irregular in shape is visible, corresponding to the region oc-
cupied by the Leo IV dSph. The black circle shows the half-light
radius of Leo IV, according to B07. The peripheral location of
V3 is remarkable, and provides further hints on the elongation
and rather deformed morphology of the Leo IV dSph.
The average apparent magnitude of the galaxy’s RR Lyrae
stars is VRR=21.48 ±0.03 mag (standard deviation of the
mean). Assuming MV=0.59 ±0.03 mag for the absolute
luminosity of the RR Lyrae stars at [Fe/H] =−1.5 (Cacciari &
Clementini 2003), ΔMV/Δ[Fe/H] =0.214 ±0.047 mag dex−1
for the slope of the luminosity–metallicity relation of RR Lyrae
stars (Clementini et al. 2003), E(B−V)=0.04 ±0.01 mag and
[Fe/H] =−2.31 (Simon & Geha 2007), the distance modulus
of Leo IV is μ0=20.94 ±0.07 mag which corresponds to a
distance d=154 ±5 kpc. The error includes uncertainties in
the photometry, reddening, metallicity, and RR Lyrae absolute
magnitude, but does not take into account evolution off the
zero-age HB which might contribute an additional 0.05 mag
uncertainty, bringing the total error budget to 0.09 mag. This
new, precise distance estimate agrees very well with the distance
of 160+15
−14 kpc derived by B07.
5. SUMMARY AND CONCLUSIONS
We have identified and obtained B,V light curves for three
fundamental-mode RR Lyrae stars (V1, V2, and V3) and one
SX Phe variable (V4) in the Leo IV dSph galaxy. In the period–
amplitude diagram V1 and V3 fall close to the loci of Oo I
Galactic GCs and bona fide regular variables in the Galactic GC
M3, while V2 lies close to the loci of Oo II and well evolved M3
RRab stars. However, their average period, Pab=0.655 days,
would suggest an Oosterhoff II classification for the galaxy.
From the average magnitude of the galaxy’s RR Lyrae stars,
the distance modulus of the Leo IV dSph is μ0=20.94 ±
0.07 mag (d=154 ±5 kpc). One of the RR Lyrae stars (V3)
lies at about 12 arcmin from the galaxy center. Nevertheless, the
mean magnitude places the star exactly on the galaxy HB and
close to the other two RRab stars, thus suggesting a significant
elongation of the Leo IV galaxy.
We thank Evan Kirby and Joshua Simon for sending us iden-
tification and individual metallicities for member stars of the
Leo IV dSph galaxy. Financial support for this study was pro-
vided by PRIN INAF 2006 (PI: G. Clementini). H.A.S. thanks
the Center for Cosmic Evolution and the U.S. NSF for support
under grant AST0607249. M.C. is supported by Proyecto Basal
PFB-06/2007, by FONDAP Centro de Astrof´
ısica 15010003,
by Proyecto FONDECYT Regular #1071002, and by a John
Simon Guggenheim Memorial Foundation Fellowship. T.C.B.
acknowledges partial support from grants PHY 02-16783 and
PHY 08-22648: Physics Frontier Center/Joint Institute for Nu-
clear Astrophysics (JINA), awarded by the US National Science
Foundation.
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