Living with a dM Star: Evolution over Time of Dynamo: Generated X-ray UV Emissions and Effects on Hosted Planets

We report on a multi-frequency study of dM stars with ages from <30 Myr to 13 Gyr. The goals are to understand the magnetic activity, coronal physics, and XUV spectral irradiances of dM stars with widely different rotations, ages, and widely different levels of XUV emissions. Because of the large number of dM stars (>70% of all stars), and their very long lifetimes, there should be numerous dM stars hosting planets. Thus dM stars are attractive targets of extrasolar planet search missions such as COROT, Kepler, SIM, and Darwin/TPF. The habitable zones (HZs) around dM stars are close to the host star (HZ 0.05-0.40 AU) making the hypothetical HZ planet strongly influenced by stellar flares, winds, and plasma ejection events that are frequent in dM stars. Also, with the long-lifetimes of dM-stars of > 20-Gyr, it might be possible for life on a HZ-planet to be much more evolved than ourselves. Of particular interest is the determination of XUV emission flux evolution with time. This is because of the critical roles that XUV coronal and chromospheric emissions play in the photoionization and photochemical evolution (and possible erosion) of planetary atmospheres and ionospheres. We have used ROSAT, ASCA, XMM and Chandra X-ray observations and combined these with EUV, and FUV-UV data (from EUVE, FUSE and IUE or HST) to form XUV spectral irradiance tables of dM stars covering a wide range of ages and XUV fluxes. These results are critical to the studies of XUV radiation of dM-stars and its effects on the environments of possible hosted extrasolar planets and on the possible origin and evolution of extraterrestrial life on such planets. The initial results of this study will be presented and discussed.

This research is supported by grants from NASA/FUSE and NSF which we gratefully acknowledge.