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

TL;DR

This study identifies 552 mid-infrared sources in the Galactic mid-plane with suspected variability by comparing data from the Spitzer and MSX surveys, highlighting potential AGB stars and confirming variability in some cases.

Contribution

It provides a new catalog of variable mid-infrared sources by carefully addressing survey differences and validating variability with additional data and spectral analysis.

Findings

At least 25% of the sources are truly variable.

At least half of the 40 selected sources show confirmed variability.

Most sources are likely Asymptotic Giant Branch stars.

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.