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The Evolution Of Massive Young Stellar Objects in the Large Magellanic Cloud. I. Identification and Spectral Classification

Seale, Jonathan P. and Looney, Leslie W. and Chu, You-Hua and Gruendl, Robert A. and Brandl, Bernhard and Chen, C.-H. Rosie and Brandner, Wolfgang and Blake, Geoffrey A. (2009) The Evolution Of Massive Young Stellar Objects in the Large Magellanic Cloud. I. Identification and Spectral Classification. Astrophysical Journal, 699 (1). pp. 150-167. ISSN 0004-637X.

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We present and categorize Spitzer infrared spectrometer spectra of 294 objects in the Large Magellanic Cloud (LMC) to create the largest and most complete catalog of massive young stellar object (YSO) spectra in the LMC. Target sources were identified from infrared photometry and multiwavelength images indicative of young, massive stars highly enshrouded in their natal gas and dust clouds. Several objects have been spectroscopically identified as non-YSOs and have features similar to more-evolved stars such as red supergiants, asymptotic giant branch (AGB), and post-AGB stars. Our sample primarily consists of 277 objects we identify as having spectral features indicative of embedded YSOs. The remaining sources are comprised of seven C-rich evolved sources, eight sources dominated by broad silicate emission, and one source with multiple broad emission features. Those with YSO-like spectra show a range of spectral features including polycyclic aromatic hydrocarbon emission, deep silicate absorption, fine-structure lines, and ice absorption features. Based upon the relative strengths of these features, we have classified the YSO candidates into several distinct categories using the widely used statistical procedure known as principal component analysis. We propose that these categories represent a spectrum of evolutionary stages during massive YSO formation. Using our catalog we put statistical constraints on the relative evolutionary timescale of processes involved in massive star formation. We conclude that massive pre-main-sequence stars spend a majority (possibly as high as 90%) of their massive, embedded lives emitting in the UV. Half of the sources in our study have features typical of compact H II regions, suggesting that massive YSOs can create a detectable compact H II region half-way through the formation time present in our sample. This study also provides a check on commonly used source-selection procedures including the use of photometry to identify YSOs. We determine that a high success rate (>95%) of identifying objects with YSO-like spectra can be achieved through careful use of infrared color-magnitude diagrams, spectral energy distributions, and image inspections.

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Blake, Geoffrey A.0000-0003-0787-1610
Additional Information:© 2009 The American Astronomical Society. Received 2009 February 6; accepted 2009 April 20; published 2009 June 10. The authors thank the anonymous referee for useful comments, Charles Gammie for an early helpful discussion of PCA, and Karna Desai and Ryan Peterson for their work on some of the figures and tables presented here. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. This study made use of observations obtained at Cerro Tololo Inter-American Observatory, a division of the National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. This publication has made use of the data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by NASA and the NSF. The CO maps are the result of the NANTEN project which is based on the mutual agreement between Nagoya University and the Carnegie Institution of Washington. This research made use of the SIMBAD database, operated at CDS, Strasbourg, France and SAOImage DS9, developed by Smithsonian Astrophysical Observatory. Support for this work was provided by NASA through an award issued by JPL/Caltech. Facilities: Spitzer (IRS, IRAC, MIPS).
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Subject Keywords:galaxies: individual (LMC); infrared: stars; instrumentation: spectrographs; Magellanic Clouds; stars: evolution; stars: formation
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Official Citation:The Evolution Of Massive Young Stellar Objects in the Large Magellanic Cloud. I. Identification and Spectral Classification Jonathan P. Seale, Leslie W. Looney, You-Hua Chu, Robert A. Gruendl, Bernhard Brandl, C.-H. Rosie Chen, Wolfgang Brandner, and Geoffrey A. Blake 2009 ApJ 699 150-167 doi: 10.1088/0004-637X/699/1/150.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15773
Deposited By: Tony Diaz
Deposited On:15 Sep 2009 17:23
Last Modified:03 Oct 2019 01:02

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