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NIR two-color diagram of H$\alpha$ emission stars in the W 5 E region. H$\alpha$ stars in A, B, and C are shown as solid triangles, solid circles, and open circles, respectively.
Source publication
We have made a new survey of emission-line stars in the W 5 E H ii region to investigate the population of PMS stars near the OB stars by using the Wide Field Grism Spectrograph 2 (WFGS2).
A total of 139 H$\alpha$ emission stars were detected and their $g'i'$-photometry was performed. Their spatial distribution shows three aggregates, i.e., two agg...
Contexts in source publication
Context 1
... the transformation equations by Carpenter (2001), we converted NIR colors of Hα stars identified with the 2MASS Point Source Catalog into the CIT system. Hα stars detected in J,H,K s bands with good quality (AAA) and the photometric error less than 0.1 magnitude are plotted in figure 4. The Hα emission stars in the groups A, B, and C are shown as solid triangles, solid circles, and open circles, respectively. ...
Context 2
... comparison, Class II sources, which have NIR colors explaining as the reddened TTS between two parallel reddening line and above the TTS dereddened locus (Meyer et al. 1997) in figure 4, are selected from the 2MASS catalog. We again used the stars or sources with good quality, and photometric color error < 0.1 mag. ...
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Throughout the last decade sensitive infrared observations obtained by the
Spitzer Space Telescope significantly increased the known population of YSOs
associated with nearby molecular clouds. With such a census recent studies have
characterized pre-main sequence stars (PMS) and determined parame- ters from
different wavelengths. Given the restrict...
Citations
A H ii region is a kind of emission nebula, and more definite samples of H ii regions can help study the formation and evolution of galaxies. Hence, a systematic search for H ii regions is necessary. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) conducts medium-resolution spectroscopic surveys and provides abundant valuable spectra for unique and rare celestial body research. Therefore, the medium-resolution spectra of LAMOST are an ideal data source for searching for Galactic H ii regions. This study uses the LAMOST spectra to expand the current spectral sample of Galactic H ii regions through machine learning. Inspired by deep convolutional neural networks with wide first-layer kernels (WDCNN), a new spectral-screening method, multihead WDCNN, is proposed and implemented. Infrared criteria are further used for the identification of Galactic H ii region candidates. Experimental results show that the multihead WDCNN model is superior to other machine-learning methods and it can effectively extract spectral features and identify H ii regions from the massive spectral database. In the end, among all candidates, 57 H ii regions are identified and known in SIMBAD, and four objects are identified as “to be confirmed” Galactic H ii region candidates. The known H ii regions and H ii region candidates can be retrieved from the LAMOST website.
We present Spitzer, near-IR (NIR) and millimetre observations of the massive star-forming regions W5-east, S235, S252, S254-S258 and NGC 7538.
Spitzer data is combined with NIR observations to identify and classify the young population while 12CO and 13CO observations are used to examine the parental molecular cloud. We detect in total 3021 young stellar objects (YSOs). Of
those, 539 are classified as Class I, and 1186 as Class II sources. YSOs are distributed in groups surrounded by a more scattered
population. Class I sources are more hierarchically organized than Class II and associated with the most dense molecular material.
We identify in total 41 embedded clusters containing between 52 and 73 per cent of the YSOs. Clusters are in general non-virialized,
turbulent and have star formation efficiencies between 5 and 50 per cent. We compare the physical properties of embedded clusters
harbouring massive stars (MEC) and low-mass embedded clusters (LEC) and find that both groups follow similar correlations
where the MEC are an extrapolation of the LEC. The mean separation between MEC members is smaller compared to the cluster
Jeans length than for LEC members. These results are in agreement with a scenario where stars are formed in hierarchically
distributed dusty filaments where fragmentation is mainly driven by turbulence for the more massive clusters. We find several
young OB-type stars having IR-excess emission which may be due to the presence of an accretion disc.
Aims: We examined the physical properties of molecular clouds (morphology, column density, number density, mass) to investigate the mechanism of triggered star formation by UV radiation from a massive star. Methods: We made extensive, high-resolution maps of molecular clouds associated and interacting with the W5-East H ii region using the 45-m telescope at the Nobeyama Radio Observatory (HPBW = 15.6 arcsec) in 13CO (J = 1-0) and C18O (J = 1-0) to reveal details in the high-density regions of the molecular clouds. In addition, to investigate the spatial distributions of young stellar objects (YSOs) in the W5-East H ii region, we mapped the spatial distributions of Class I and II candidates. Results: We identified eight 13CO molecular clouds (three of them are known bright-rimmed clouds) and nine 18O clumps. The masses of the clouds and clumps range from 460 to 36 000 M&sun; and from 55 to 740 M&sun;, respectively. The peak 13CO column densities of the clouds facing the H ii region are twice as large as the others. They have steep density gradients toward the H ii region, indicating interactions with the H ii region. We selected 55 Class I candidates and 778 Class II candidates associated with the W5-East H ii region from the previous Spitzer IRAC/MIPS survey. Most Class I candidates are located around integrated intensity peaks of 13CO, whereas most Class II candidates are distributed along the front sides of the BRC arcs close to the exciting star. Conclusions: The alignments of the YSO candidates and the molecular clouds in order of age indicate that triggered star formation occurs in the W5-East H ii region as a result of gas compression by strong UV radiation. Based on the column densities of 13CO and the spatial distribution of YSO candidates, we identified a new bright-rimmed cloud candidate on the west side of the W5-East H ii region.
W5-E has been observed with the Herschel-PACS and -SPIRE photometers, at 100,
160, 250, 350, and 500 microns. The dust temperature map shows a rather uniform
temperature, in the range 17.5-20 K in the dense condensations or filaments,
21-22 K in the photodissociation regions, and 24-31 K in the direction of the
ionized regions. The column densities are rather low, everywhere lower than
10^23 cm-2, and of the order of a few 10^21 cm-2 in the PDRs. About 8000 solar
masses of neutral material surrounds the ionized region, which is low with
respect to the volume of this HII region; we suggest that the exciting stars of
the W5-E, W5-W, Sh~201, A and B HII regions formed along a dense filament or
sheet rather than inside a more spherical cloud. Fifty point sources have been
detected at 100 microns. Most of them are Class 0/I YSOs. The SEDs of their
envelopes have been fitted using a modified blackbody model. These envelopes
are cold, with a mean temperature of 15.7+-1.8K. Their masses are in the range
1.3-47 solar masses. Eleven of these point sources are candidate Class 0 YSOs.
Twelve of these point sources are possibly at the origin of bipolar outflows
detected in this region. None of the YSOs contain a massive central object, but
a few may form a massive star as they have both a massive envelope and also a
high envelope accretion rate. Most of the Class 0/I YSOs are observed in the
direction of high column density material, for example in the direction of the
massive condensations present at the waist of the bipolar Sh 201 HII region or
enclosed by the bright-rimmed cloud BRC14. The overdensity of Class 0/I YSOs on
the borders of the HII regions strongly suggests that triggered star formation
is at work in this region but, due to insufficient resolution, the exact
processes at the origin of the triggering are difficult to determine.
The aim of this paper is to present the results of photometric investigations of the central cluster of the W5 E H ii region as well as a follow-up study of the triggered star formation in and around bright-rimmed clouds (BRCs). We have carried
out wide-field UBVIC and deep VIC photometry of the W5 E H ii region. A distance of ∼2.1 kpc and a mean age of ∼1.3 Myr have been obtained for the central cluster. The young stellar objects
(YSOs) associated with the region are identified on the basis of near-infrared and mid-infrared observations. We confirmed
our earlier results that the average age of the YSOs lying on/inside the rim is younger than those lying outside the rim.
The global distribution of the YSOs shows an aligned distribution from the ionizing source to the BRCs. These facts indicate
that a series of radiation-driven implosion processes proceeded from near the central ionizing source towards the periphery
of the W5 E H ii region. We found that, in general, the age distributions of the Class II and Class III sources are the same. This result
is apparently in contradiction to the conclusion by Bertout, Siess & Cabrit and Chauhan et al. that classical T Tauri stars
evolve to weak-line T Tauri stars. The initial mass function of the central cluster region in the mass range 0.4 ≤M/M⊙≤ 30 can be represented by Γ=−1.29 ± 0.04. The cumulative mass functions indicate that in the mass range 0.2 ≤M/M⊙≤ 0.8, the cluster region and BRC NW have more low-mass YSOs compared to BRCs 13 and 14.
We have made an extensive survey of emission-line stars in the IC 1396 H II region to investigate the low-mass population of pre-main-sequence (PMS) stars. A total of 639 Hα emission-line stars were detected in an area of 4.2 deg2 and their i' photometry was measured. Their spatial distribution exhibits several aggregates near the elephant trunk globule (Rim A) and bright-rimmed clouds at the edge of the H II region (Rim B and SFO 37, 38, 39, 41), and near HD 206267, which is the main exciting star of the H II region. Based on the extinction estimated from the near-infrared color-color diagram, we have selected PMS star candidates associated with IC 1396. The age and mass were derived from the extinction-corrected color-magnitude diagram and theoretical PMS tracks. Most of our PMS candidates have ages of <3 Myr and masses of 0.2-0.6 M
☉. Although it appears that only a few stars were formed in the last 1 Myr in the east region of the exciting star, the age difference among subregions in our surveyed area is not clear from the statistical test. Our results may suggest that massive stars were born after the continuous formation of low-mass stars for 10 Myr. The birth of the exciting star could be the late stage of slow but contiguous star formation in the natal molecular cloud. It may have triggered the formation of many low-mass stars at the dense inhomogeneity in and around the H II region by a radiation-driven implosion.
Using photometric data of infrared surveys, young stellar object (YSO) status is verified for 141 objects selected in our previous papers in the Cassiopeia and Camelopardalis segment of the Milky Way bounded by Galactic coordinates (l, b) = (132--158 deg, p/m 12 deg). The area includes the known star-forming regions in the emission nebulae W3, W4 and W5 and the massive YSO AFGL 490. Spectral energy distribution (SED) curves between 700 nm and 160 microns, constructed from the GSC2, 2MASS, IRAS, MSX, Spitzer and AKARI data, are used to estimate the evolutionary stages of these stars. We confirm the YSO status for most of the objects. If all of the investigated objects were YSOs, 45 % of them should belong to Class I, 41 % to class II and 14 % to Class III. However, SEDs of some of these objects can be affected by nearby extended infrared sources, like compact H II regions, infrared clusters or dusty galaxies. Comment: 33 pages, 2 figures
The aim of this paper is to quantitatively testify the "{\it small-scale sequential star formation}" hypothesis in and around bright-rimmed clouds (BRCs). As a continuation of the recent attempt by Ogura et al. (2007, Paper I), we have carried out $BVI_{c}$ photometry of four more BRC aggregates along with deeper re-observations of 2 previously observed BRCs. Again quantitative age gradients are found in almost all the BRCs studied in the present work. Archival Spitzer/IRAC data also support this result. The global distribution of NIR excess stars in each HII region studied here clearly shows evidence that a series of radiation driven implosion (RDI) processes proceeded in the past from near the central O star(s) towards the peripheries of the HII region. We found that in general weak-line T-Tauri stars (WTTSs) are somewhat older than classical T-Tauri stars (CTTSs). Also the fraction of CTTSs among the T-Tauri stars (TTSs) associated with the BRCs is found to decrease with age. These facts are in accordance with the recent conclusion by Bertout et al. (2007) that CTTSs evolve into WTTSs. It seems that in general the EW of H$\alpha$ emission in TTSs associated with the BRCs decreases with age. The mass function (MF) of the aggregates associated with the BRCs of the morphological type "A" seems to follow that found in young open clusters, whereas "B/C" type BRCs show significantly steeper MF.
We present images and initial results from our extensive Spitzer Space Telescope imaging survey of the W5 H II region with the Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS). We detect dense clusters of stars, centered on the O stars: HD 18326, BD +60 586, HD 17505 and HD 17520. At 24 microns substantial extended emission is visible, presumably from heated dust grains that survive in the strongly ionizing environment of the H {\sc ii} region. With photometry of more than 18000 point sources, we analyze the clustering properties of objects classified as young stars by their IR spectral energy distributions (a total of 2064 sources) across the region using a minimal-spanning-tree algorithm. We find ~40--70% of infrared excess sources belong to clusters with >10 members. We find that within the evacuated cavities of the H II regions that make up W5, the ratio of Class II to Class I sources is ~7 times higher than for objects coincident with molecular gas as traced by 12CO emission and near-IR extinction maps. We attribute this contrast to an age difference between the two locations, and postulate that at least two distinct generations of star formation are visible across W5. Our preliminary analysis shows that triggering is a plausible mechanism to explain the multiple generations of star formation in W5, and merits further investigation. Comment: 14 pages, 11 color figures. To appear in December 1st edition of ApJ
