MEASUREMENTS OF THE WINDS OF SOLAR-LIKE STARS AND THEIR INFLUENCE ON EXTRASOLAR PLANETS

摘要

Until recently there have been no reliable measurements of the mass loss rates for main sequence stars of spectral type F-M. Although such mass loss rates are generally presumed to be small as in the solar case, there has been no confirmation of this assumption. We report on a new method for measuring dwarf star mass loss rates using the observed absorption on the blue side of the interstellar Lyman-α absorption feature to study the star's astrosphere. Astrospheres, which are analogs of the heliosphere, are produced when the stellar wind interacts with the interstellar gas flow. Neutral hydrogen piles up at the astropause when the interstellar hydrogen atoms charge exchange with the stellar wind protons. This absorption is blue-shifted with respect to the interstellar medium flow. Astrosphere models constructed to be consistent with the absorption features of eight dwarf stars provide mass loss rates and show a dependence of mass loss rate per unit surface area on X-ray surface flux and thus stellar age. We infer a relation of mass loss rate with age for solar-like stars, and discuss its implications for planets around the Sun and stars.