Early-stage young stellar objects in the Small Magellanic Cloud

被引：59

作者：

Oliveira, J. M. ^{[1
]}

van Loon, J. Th ^{[1
]}

Sloan, G. C. ^{[2
]}

Sewilo, M. ^{[3
]}

Kraemer, K. E. ^{[4
]}

Wood, P. R. ^{[5
]}

Indebetouw, R. ^{[6
,7
]}

Filipovic, M. D. ^{[8
]}

Crawford, E. J. ^{[8
]}

Wong, G. F. ^{[8
]}

Hora, J. L. ^{[9
]}

Meixner, M. ^{[10
]}

Robitaille, T. P. ^{[11
]}

Shiao, B. ^{[10
]}

Simon, J. D. ^{[12
]}

机构：

[1] Keele Univ, Lennard Jones Labs, Sch Phys & Geog Sci, Keele ST5 5BG, Staffs, England

[2] Cornell Univ, Dept Astron, Ithaca, NY 14853 USA

[3] Johns Hopkins Univ, Dept Phys & Astron, Baltimore, MD 21218 USA

[4] Boston Coll, Inst Sci Res, Chestnut Hill, MA 02467 USA

[5] Australian Natl Univ, Res Sch Astron & Astrophys, Weston, ACT 2611, Australia

[6] Univ Virginia, Dept Astron, Charlottesville, VA 22903 USA

[7] Natl Radio Astron Observ, Charlottesville, VA 22904 USA

[8] Univ Western Sydney, Penrith, NSW 1797, Australia

[9] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA

[10] Space Telescope Sci Inst, Baltimore, MD 21218 USA

[11] Max Planck Inst Astron, D-69117 Heidelberg, Germany

[12] Observ Carnegie Inst Washington, Pasadena, CA 91101 USA

来源：

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY | 2013年 / 428卷 / 04期

关键词：

astrochemistry; circumstellar matter; stars: formation; stars: protostars; galaxies: individual: SMC; Magellanic Clouds; SPITZER-IRS SPECTRA; T-TAURI STARS; 20-CM RADIO-CONTINUUM; ARRAY CAMERA IRAC; GALAXY EVOLUTION; LOW METALLICITY; ENERGY-DISTRIBUTIONS; SPECTROSCOPIC SURVEY; ISO SPECTROSCOPY; ICE CHEMISTRY;

D O I：

10.1093/mnras/sts250

中图分类号：

P1 [天文学];

学科分类号：

0704 ;

摘要：

We present new observations of 34 young stellar object (YSO) candidates in the Small Magellanic Cloud (SMC). The photometric selection required sources to be bright at 24 and 70 mu m (to exclude evolved stars and galaxies). The anchor of the analysis is a set of Spitzer Infrared Spectrograph (IRS) spectra, supplemented by ground-based 3-5 mu m spectra, Spitzer Infrared Array Camera and Multiband Imaging Photometer for Spitzer photometry, near-infrared (IR) imaging and photometry, optical spectroscopy and radio data. The sources' spectral energy distributions and spectral indices are consistent with embedded YSOs; prominent silicate absorption is observed in the spectra of at least 10 sources, silicate emission is observed towards four sources. Polycyclic aromatic hydrocarbon (PAH) emission is detected towards all but two sources. Based on band ratios (in particular the strength of the 11.3-mu m and the weakness of the 8.6-mu m bands) PAH emission towards SMC YSOs is dominated by predominantly small neutral grains. Ice absorption is observed towards 14 sources in the SMC. The comparison of H2O and CO2 ice column densities for SMC, Large Magellanic Cloud and Galactic samples suggests that there is a significant H2O column density threshold for the detection of CO2 ice. This supports the scenario proposed by Oliveira et al., where the reduced shielding in metal-poor environments depletes the H2O column density in the outer regions of the YSO envelopes. No CO ice is detected towards the SMC sources. Emission due to pure rotational 0-0 transitions of molecular hydrogen is detected towards the majority of SMC sources, allowing us to estimate rotational temperatures and H-2 column densities. All but one source are spectroscopically confirmed as SMC YSOs. Based on the presence of ice absorption, silicate emission or absorption and PAH emission, the sources are classified and placed in an evolutionary sequence. Of the 33 YSOs identified in the SMC, 30 sources populate different stages of massive stellar evolution. The presence of ice- and/or silicate-absorption features indicates sources in the early embedded stages; as a source evolves, a compact H II region starts to emerge, and at the later stages the source's IR spectrum is completely dominated by PAH and fine-structure emission. The remaining three sources are classified as intermediate-mass YSOs with a thick dusty disc and a tenuous envelope still present. We propose one of the SMC sources is a D-type symbiotic system, based on the presence of Raman, H and He emission lines in the optical spectrum, and silicate emission in the IRS spectrum. This would be the first dust-rich symbiotic system identified in the SMC.

引用

页码：3001 / 3033

页数：33

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