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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
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:
FileName Lrecl Records Explanations
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
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
Bytes Format Units Label Explanations
1- 2 I2 --- Seq Running sequence number 4- 22 A19 --- [GC2009] Identification from Gruendl & Chu, 2009, Cat. J/ApJS/184/172 ( 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; <DEM L NNNa> 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
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, <LHA 120-N NNNA> 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). Note (4): Nearby OB associations (Lucke & Hodge 1970AJ.....75..171L; <LH NNN> in Simbad).
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 19 A19 --- [GC2009] YSO identification ( 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)
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.
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
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)
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.
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 2 I2 --- Seq Running sequence number 4- 22 A19 --- [GC2009] Source identification ( 23 A1 --- f_[GC2009] [*] *: Object also in table 1; Seq 15 (flag added by CDS) 25- 64 A40 --- Type Description of the source
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
History: From electronic version of the journal
(End) Emmanuelle Perret [CDS] 05-Jan-2012
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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