M Class Dwarfs as Host Stars

Planetary host stars: Evaluating uncertainties in ultra-cool model atmospheres

Authors:

Bozhinova et al

Abstract:

M-dwarfs are discussed as promising targets for detecting planet at the lower mass end of the planetary mass distribution. An important step in this process is to accurately estimate the stellar parameters of the M-dwarf host star for which the results of stellar model atmosphere simulations are used. We present a comparison of the ATLAS9, MARCS, PHOENIX and Drift-PHOENIX model atmosphere families in the M-dwarf parameter space. We examine the differences in the (Tgas, pgas)-structures, in synthetic photometric fluxes and in colour indices. We compiled the broad-band synthetic photometric fluxes for all available M-dwarf model atmospheres for the UKIRT WFCAM ZYJHK, 2MASS JHKs and Johnson UBVRI filters, and calculated related colour indices. We find that the synthetic colours in the IR wavelengths diverge by no more than 0.15 dex amongst all model families. For all bands considered, discrepancies in colour diminish for the higher Teff-end of model atmosphere grids. We notice significant differences in colours between all model families and observed data, incl. Kepler 42 and GJ1214 as examples. We explore the impact of these uncertainties of the atmosphere models on the planet's equilibrium temperatures and on the location of the habitable zone. For GJ1214, an uncertainty of 100K in Teff causes a change of 17K in the planet's equilibrium temperature. The location of the habitable zone is in good agreement between Drift-PHOENIX and MARCS, a deviation of 0.01 - 0.02 AU occurs for PHOENIX model atmospheres.