Name/Affiliation: Christopher Theissen (Boston University)
WISE Infrared Excess Detections for SDSS M Dwarfs: Cool Field Stars with Evidence of Warm Circumstellar Material
We investigate the mid-infrared properties of low-mass field dwarfs, combining M dwarfs from the SDSS DR7 spectroscopic and DR10 photometric catalogs with photometry from the AllWISE source catalog. For the spectroscopic sample, we developed SDSS and WISE color-color selection criteria to select 300 M dwarfs (from the 70,841 in the DR7 catalog) that exhibit infrared flux above typical M dwarf photosphere levels at 12 and/or 22 µm. We also find 30 stars within the footprint of the Orion OB1 association that have not been previously identified. Using synthetic photometry, we characterize the dust populations inferred from each infrared excess, and find high fractional infrared luminosities (~0.01 L?) and orbital distances within the snow line (< 1 AU). Using the SDSS spectra, we measure surface gravity dependent features, and examine tracers of youth (Ha, UV emission, and Li absorption). Less than 6% of our sample shows a reliable indication of youth, implying a stellar population with ages > 1 Gyr. Our results imply that, due to the orbital distances of our inferred dust populations and the penchant for low-mass stars to create terrestrial planets, the most likely cause of dust in these systems is planetary collisions. A similar result has been used to explain the dust population observed around the older field star BD+20 307 (= 1 Gyr; Weinberger et al. 2011). We also present preliminary results using the DR10 photometric M dwarf sample. This sample, consisting of millions of M dwarfs, allows us to examine the phenomena of field M dwarfs exhibiting infrared excesses in a Galactic context.