J/ApJ/707/1417 HST view of YSOs in the LMC (Vaidya+, 2009)
A Hubble space telescope view of the interstellar environments of young stellar
objects in the Large Magellanic Cloud.
Vaidya K., Chu Y.-H., Gruendl R.A., Chen C.-H.R., Looney L.W.
<Astrophys. J., 707, 1417-1426 (2009)>
=2009ApJ...707.1417V 2009ApJ...707.1417V
ADC_Keywords: H II regions ; Magellanic Clouds ; Molecular clouds ; YSOs
Photometry, H-alpha
Keywords: H II regions - Magellanic Clouds - stars: formation
Abstract:
We have used archival Hubble Space Telecope (HST) Hα images to
study the immediate environments of massive and intermediate-mass
young stellar object (YSO) candidates in the Large Magellanic Cloud
(LMC). The sample of YSO candidates, taken from Gruendl & Chu (2009,
Cat. J/ApJS/184/172), was selected based on Spitzer IRAC and MIPS
observations of the entire LMC and complementary ground-based optical
and near-infrared observations. We found HST Hα images for 99
YSO candidates in the LMC, of which 82 appear to be genuine YSOs. More
than 95% of the YSOs are found to be associated with molecular clouds.
YSOs are seen in three different kinds of environments in the Hα
images: in dark clouds, inside or on the tip of bright-rimmed dust
pillars, and in small HII regions. Comparisons of spectral energy
distributions for YSOs in these three different kinds of environments
suggest that YSOs in dark clouds are the youngest, YSOs with small HII
regions are the most evolved, and YSOs in bright-rimmed dust pillars
span a range of intermediate evolutionary stages. This rough
evolutionary sequence is substantiated by the presence of silicate
absorption features in the Spitzer Infrared Spectrograph spectra of
some YSOs in dark clouds and in bright-rimmed dust pillars, but not
those of YSOs in small HII regions. We present a discussion on
triggered star formation for YSOs in bright-rimmed dust pillars or in
dark clouds adjacent to HII regions. As many as 50% of the YSOs are
resolved into multiple sources in high-resolution HST images.
Description:
We searched the HST archive for Hα images observed with the Wide
Field Planetary Camera 2 (WFPC2) and the Advanced Camera for Surveys
(ACS) for a field of ∼78deg2 centered on the LMC coordinates
(J0518-6834), available as of 2008 August. We have been imaging YSO
candidates in selected regions throughout the LMC in the near-infrared
J and Ks bands with the IR Side Port Imager (ISPI) on the Blanco 4m
telescope at the Cerro Tololo Inter-American Observatory in 2008
January for additional confirmation on the nature of the YSO
candidates.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 82 76 Properties of YSOs with HST Hα images
table2.dat 73 8 Properties of resolved HII regions associated
with massive YSOs
table3.dat 46 14 Properties of marginally resolved and unresolved
HII regions associated with massive YSOs
table4.dat 64 17 List of non-YSOs
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See also:
VII/232 : Nebulae in the Magellanic Clouds (Davies+ 1976)
J/A+A/518/L73 : Youngest massive protostars in the LMC (Sewilo+, 2010)
J/ApJS/184/172 : High- and intermediate-mass YSOs in the LMC (Gruendl+, 2009)
J/ApJ/699/150 : Spectral classifications of Massive YSOs in LMC (Seale+, 2009)
J/ApJS/184/1 : Molecular clouds in the LMC by NANTEN. II. (Kawamura+, 2009)
J/ApJ/695/511 : Young massive stars in LHA 120-N 44 (Chen+, 2009)
J/ApJS/178/56 : CO observations of LMC Giant Molecular clouds (Fukui+, 2008)
J/AJ/136/18 : LMC SAGE. New candidate YSOs (Whitney+, 2008)
J/PASJ/53/971 : CO catalog of LMC molecular clouds (Mizuno+, 2001)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq Running sequence number
4- 22 A19 --- [GC2009] Identification from Gruendl & Chu, 2009,
Cat. J/ApJS/184/172 (JHHMMSS.ss+DDMMSS.s)
24- 32 A9 --- Cat Category of the environment (G1)
34- 36 A3 --- f_Cat [cd, ] Flag(s) on Cat (1)
38- 44 A7 --- DEM Associated HII region from Davies et al.
(1976, Cat. VII/232; in Simbad)
46- 50 A5 --- LHA120 Associated HII region from Henize (2)
52- 54 A3 --- CO? [Yes/No ] CO detection (3)
56- 60 A5 --- LH Nearby OB association (4)
62- 68 A7 --- IRS Spitzer/IRS classification of the YSO (G2)
70- 72 A3 --- Si? [Yes/No ] Si absorption feature in IRS spectra
74- 79 A6 --- YSO YSO type
81- 82 A2 --- Fig Figure number in the paper
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Note (1): Flag as follows:
c = More than one YSOs is discovered in the Spitzer PSF.
d = YSOs are found in more than one kind of environment, e.g. 2/3b refers
to YSOs which are associated with bright-rimmed dust pillars and the
optical counterpart is a small HII region.
Note (2): Name of the associated HII region from Henize, 1956ApJS....2..315H 1956ApJS....2..315H,
in Simbad.
Note (3): Indication of whether the YSO is associated with molecular clouds
detected by the NANTEN survey (Fukui et al. 2001PASJ...53L..41F 2001PASJ...53L..41F).
Note (4): Nearby OB associations (Lucke & Hodge 1970AJ.....75..171L 1970AJ.....75..171L;
in Simbad).
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- [GC2009] YSO identification (JHHMMSS.ss+DDMMSS.s)
21- 24 F4.2 pc Lgth Length (1)
26- 33 E8.3 mW/m2 FHa Hα flux not corrected for extinction
35- 40 E6.3 pc/cm6 EM Emission measure of the HII region
42- 44 I3 cm-3 ne rms electron density
46- 52 E7.3 10-7W LHa Hα luminosity (2)
54- 60 E7.3 ph/s Q(H0) Ionizing power (Q(H0)) in photons/s (2)
62- 65 A4 --- SpT MK spectral type (2)
67- 73 A7 --- IRS Spitzer/IRS classification of the YSO (G2)
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Note (1): Average emitting path lengths of the HII regions.
Note (2): Note that the Hα luminosities, ionizing powers, and the spectral
types are lower limits to these quantities, as we have not applied an
extinction correction.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- [GC2009] YSO identification (1)
21- 22 A2 --- Cat Category of the environment (G1)
24- 30 E7.2 mW/m2 FHa Observed Hα flux
32- 38 E7.2 mW/m2 Fc ? Expected continuum flux of the YSO in the
Hα passband
40- 46 A7 --- IRS Spitzer/IRS classification of the YSO (G2)
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Note (1): J053943.80-693834.0 is J053943.82-693834.0 in Gruendl & Chu, 2009,
Cat. J/ApJS/184/172 and Simbad; corrected at CDS.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq Running sequence number
4- 22 A19 --- [GC2009] Source identification (JHHMMSS.ss+DDMMSS.s)
23 A1 --- f_[GC2009] [*] *: Object also in table 1; Seq 15 (flag
added by CDS)
25- 64 A40 --- Type Description of the source
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Global notes:
Note (G1): Category describes YSO environments as follows:
1a = YSOs found in dark clouds without optical counterparts in HST
Hα images
1b = YSOs in dark clouds with optical counterparts
2 = YSOs in bright rimmed dust pillars
3a = YSOs with resolved HII regions
3b = YSOs with marginally resolved HII regions
3c = YSOs with unresolved HII regions
Note (G2): Classification by Seale et al. (2009, Cat. J/ApJ/699/150) of these
YSOs based on the Spitzer IRS spectra. The groups are defined as follows:
SE = spectra with silicate absorption and fine-structure lines
P = spectra showing Polycyclic Aromatic Hydrocarbons (PAH) emissions
PE = spectra showing both PAH emission and fine-structure lines
E = spectra showing fine-structure lines
F = spectra that appear to be featureless though they may show one or
more of the above characteristics
Unknown = embedded objects with unknown classification
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 05-Jan-2012