Are exoplanets orbiting m dwarfs extreme?

Abstract

M dwarf stars have long spin-down timescales, long activity lifetimes and persistent magnetic activity, all of which have implications for the potential habitability of orbiting planets. I will present results from several research programs investigating M dwarf rotation, activity and evolution. I will discuss a new technique to measure chemical-kinematic ages of main-sequence M dwarf stars. We applied that technique to a variety of nearby M dwarfs, both planet hosts and non-planet hosts, and rapid (young) and slow (old) rotators. We find that relatively slow rotators (P 100 days) do not appear to be α enriched, indicating that they are not over 10 Gyrs old. Second, for the rapid rotators, we see clear evidence of Zeeman enhancement of Y-band Ti I lines as a function of Rossby number. While other activity indicators, such as H-α and X-ray emission, appear to saturate with low Rossby number, Zeeman enhancement does not, indicating that the saturation mechanism is confined to the chromosphere and corona. Finally, I will present new results on the M dwarf radius problem. Using spectral synthesis methods, we find that large magnetic star spot fractions are primarily responsible for observed discrepancies between model and measured stellar radii in fully convective M dwarf stars. As most M dwarfs appear discrepant, our results suggest the vast majority of M dwarfs have large spot fractions and correspondingly high localization of magnetic fields.