Warm Dust Around Cool Stars: From Exoplanet Collisions, Failed Formation or Tidal Destruction?

Warm Dust around Cool Stars: Field M Dwarfs with WISE 12 or 22 Micron Excess Emission

Authors:

Theissen et al

Abstract:

Using the SDSS DR7 spectroscopic catalog, we searched the WISE AllWISE catalog to investigate the occurrence of warm dust, as inferred from IR excesses, around field M dwarfs (dMs). We developed SDSS/WISE color selection criteria to identify 175 dMs (from 70,841) that show IR flux greater than typical dM photosphere levels at 12 and/or 22 μm, including seven new stars within the Orion OB1 footprint. We characterize the dust populations inferred from each IR excess, and investigate the possibility that these excesses could arise from ultracool binary companions by modeling combined SEDs. Our observed IR fluxes are greater than levels expected from ultracool companions (greater than 3σ). We also estimate that the probability the observed IR excesses are due to chance alignments with extragalactic sources is less than 0.1%. Using SDSS spectra we measure surface gravity dependent features (K, Na, and CaH 3), and find less than 15% of our sample indicate low surface gravities. Examining tracers of youth (Hα, UV fluxes, and Li absorption), we find less than 3% of our sample appear young, indicating we are observing a population of field stars ≳ 1 Gyr, likely harboring circumstellar material. We investigate age-dependent properties probed by this sample, studying the disk fraction as a function of Galactic height. The fraction remains small and constant to |Z|∼700 pc, and then drops, indicating little to no trend with age. Possible explanations for disks around field dMs include: 1) collisions of planetary bodies, 2) tidal disruption of planetary bodies, or 3) failed planet formation.