Cool Stars with Extreme Mid-Infrared Excesses: Potential Tracers of Planetary Collisions

I present a sample of more than 100 low-mass field stars exhibiting significant amounts of excess infrared (IR) flux. The IR excesses are likely caused by warm dust originating from collisions between terrestrial planets or planetary embryos. Our sample has tremendous ramifications for the habitability and stability of other worlds because the collisions that create the IR excesses inform the timescale and stellar mass dependence of catastrophic events in extrasolar systems. Until recently, the samples of these systems consisted of only a handful of solar-type stars, the so-called “extreme debris disk” systems. The majority of these stars have ages coinciding with the timescale for planet formation, less than a few 100 Myr. However, one of these systems (BD +20 307), is much older (~1 Gyr), indicating that planetary collisions may occur on timescales longer than that for planet formation. Most of the stars in our sample are older and have completed the process of planet/star formation (> 1 Gyr). With the ubiquity of low-mass stars throughout the Galaxy, and their penchant for hosting multiple, close-in terrestrial planets, our sample is important for measuring the collision rate in these systems. Due to the rarity of the IR excesses (~0.1%), a large sample of high-fidelity low-mass stars is required. We use the more than 8 million stars in the Motion Verified Red Stars (MoVeRS) catalog, constructed from the combined SDSS, 2MASS, and WISE datasets, to identify low-mass stars with significant excess IR flux at 12 microns (from WISE), a tracer of warm dust (and planetary collisions) in these systems. We discuss how the existence of IR excesses varies as a function of age and mass, and discuss possible implications for the habitability of low-mass extrasolar systems