A Spectral Inventory of Massive YSOs in the LMC


First Author:
Jonathan Seale
Email: seale AT astro.uiuc.edu
Astronomy Department, University of Illinois at Urbana-Champaign
1002 West Greet Street
Urbana, IL 61801, USA
Coauthors:
Looney, Leslie, Astronomy Department, University of Illinois at Urbana-Champaign
Chu, You-Hua, Astronomy Department, University of Illinois at Urbana-Champaign
Gruendl, Robert, Astronomy Department, University of Illinois at Urbana-Champaign
Brandl, Bernhard, Astronomy Department, Leiden University
Chen, Rosie, Astronomy Department, University of Virginia
Brandner, Wolfgang, Max-Plank-Institut fur Astronomie, Planet & Star Formation
Blake, Geoff, Astronomy Department, California Institute of Technology

Abstract

We obtain, present, and categorize Spitzer IRS spectra of 294 objects in the Large Magellanic Cloud (LMC) to create the largest and most complete catalog of massive young stellar objects (YSOs) in the LMC. Target sources were identified from infrared photometry and multi-wavelength images indicative of young, massive stars highly enshrouded in their natal gas and dust. Several objects have been spectroscopically identified as non-YSOs and have features similar to more evolved stars such as red supergiants (RSG), asymptotic giant branch (AGB) and post-AGB stars. Our sample of a total of 294 sources primarily consists of 277 objects (94%) we classify as YSOs. The remaining sources are comprised of 7 C-rich evolved sources, 8 sources dominated by broad silicate emission, and 1 multiple broad emission feature-dominated source. The YSOs show a range of spectral features including polycyclic aromatic hydrocarbon (PAH) emission, deep silicate absorption, fine structure lines, and ice absorption features. Based upon the relative strengths of these features, we have further classified the YSOs into several distinct categories using the widely-used statistical procedure known as principal component analysis (PCA). We propose that these categories represent distinct evolutionary stages of a massive YSO's 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. We additionally conclude that massive YSOs will ionize a compact HII region approximately half-way though their formation.
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