The LMC’s Top 250: Classification of the Most Luminous Compact 8 µm Sources in the Large Magellanic Cloud

Joel H. Kastner, Rochester Institute of Technology
Stephen L. Thorndike, University of Rochester
Paul A. Romanczyk, Rochester Institute of Technology
Catherine Buchanan, University of Melbourne
Bruce J. Hrivnak, Valparaiso University
Raghvendra Sahai, NASA
Michael Egan, National Geospatial-Intelligence Agency

This is a pre-print of an article published by The American Astronomical Society. © 2008. The American Astronomical Society. All rights reserved. The final published version is located here:

Also archived in: arXiv:astro-ph/0703584v4

Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works in February 2014.


To ascertain the nature of the brightest compact mid-infrared sources in the Large Magellanic Cloud (LMC), we have applied an updated version of the Buchanan et al. (2006) 2MASS-MSX color classification system, which is based on the results of Spitzer Space Telescope spectroscopy, to a mid-infrared (8 μm) flux-limited sample of 250 LMC objects for which 2MASS and MSX photometry is available. The resulting 2MASS-MSX (“JHK8”) color-based classifications of these sources, which constitute the most mid-IR-luminous objects in the LMC, were augmented, cross-checked, and corrected where necessary via a variety of independent means, such that only 47 sources retain tentative classifications and only 10 sources cannot be classified at all. The sample is found to consist primarily of carbon-rich asymptotic giant branch (AGB) stars ( 35%), red supergiants ( 18%), and compact H ii regions ( 30%), with additional, small populations of oxygen-rich AGB stars ( 4%), dusty, early-type emission-line stars ( 3%), and foreground, O-rich AGB stars in the Milky Way ( 3%). The very large ratio of C-rich to O-rich objects among the luminous and heavily dust-enshrouded AGB stars in our LMC IR source sample is consistent with the hypothesis that carbon stars form easily in lower metallicity environments. We demonstrate that very luminous C-rich and O-rich AGB stars and red supergiants, identified here primarily on the basis of their JHK8 colors, also appear as distinct clusters in Spitzer IRAC/MIPS color-color diagrams. Thus, in principle, the IRS-based IR photometric classification techniques applied here to the LMC can be applied to any external galaxy whose most luminous IR point sources are detectable and resolvable by 2MASS and Spitzer.