Infrared point source variability between the Spitzer and MSX surveys of the Galactic mid-plane

Abstract

We present a list of 552 sources with suspected variability, based on a comparison of mid-infrared photometry from the GLIMPSE I and MSX surveys, which were carried out nearly a decade apart. We were careful to address issues such as the difference in resolution and sensitivity between the two surveys, as well as the differences in the spectral responses of the instruments. We selected only sources where the IRAC 8.0 and MSX 8.28 micron fluxes differ by more than a factor of two, in order to minimize contamination from sources where the difference in fluxes at 8 micron is due to a strong 10 micron silicate feature. We present a subset of 40 sources for which additional evidence suggests variability, using 2MASS and MIPSGAL data. Based on a comparison with the variability flags in the IRAS and MSX Point-Source Catalogs we estimate that at least a quarter of the 552 sources, and at least half of the 40 sources are truly variable. In addition, we tentatively confirm the variability of one source using multi-epoch IRAS LRS spectra. We suggest that most of the sources in our list are likely to be Asymptotic Giant Branch stars.

47 pages, 12 Figures, 3 Tables, accepted for publication in AJ

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• Infrared photometric study of the massive star forming region S235 using Spitzer-IRAC and JHK observations
• MSX versus IRAS Two-Color Diagrams and the CSE-Sequence of Oxygen-Rich Late-Type Stars
• A Catalog of 24um Sources Toward the Galactic Center
• On the mid-IR variability of candidate eruptive variables (EXors): a comparison between Spitzer and WISE data
• Ultracool Field Brown Dwarf Candidates Selected at 4.5 microns
• The VVV Near-IR Galaxy Catalogue beyond the Galactic disk
• New R Coronae Borealis stars discovered in OGLE-III Galactic Bulge fields from their mid- and near- infrared properties