Self-Consistent Quiescent Model Atmospheres for M Dwarfs
M dwarfs are among the most populous objects in our Galaxy, comprising roughly 70% of the stars in the Solar Neighborhood and almost half of the Galactic stellar mass. Despite this fact, their low luminosities have kept them shrouded in mystery until only the recent past, when the advent and availability of powerful telescopes and large survey programs has produced a wealth of data, exponentially increasing our understanding. However, while the abundance of data has made it possible for us to characterize these objects through photometry and spectroscopy, even necessitating the addition of spectral classes L and T to describe dwarfs cooler and less massive than M, many questions remain unanswered. In particular, magnetic activity in low mass stars is still poorly understood, especially for the latest spectral types.
Method
As persistent chromospheric, coronal and transition region emission has been found in even the lowest mass M dwarfs (Hawley & Johns-Krull, 2003), it is imperative that we understand these atmospheres in their quiescent state. To this end, I will construct self-consistent model atmospheres for M dwarfs. This effort complements recent work on modeling the outer atmospheres of M dwarfs during flaring states with a radiative-hydrodynamic version of MULTI, known as RADYN (Carlsson & Stein 1997; Abbett & Hawley 1999; Allred et al. 2005). The flare models require a quiescent atmosphere for input, and there exists no self-consistent quiescent model of an M dwarf atmosphere to date (Giampapa et al. 1982; Mauas et al. 1997). My thesis will take a two-pronged approach, utilizing both observation and theory. Using the non-LTE radiative transfer program RH (Uitenbroek 2001), I will self-consistently model quiescent M dwarf atmospheres, constraining the models with new spectral data gathered with the ARC 3.5m Telescope at Apache Point Observatory.