  Stellar winds of cool main sequence stars are very difficult to constrain
observationally. One way to measure stellar mass loss rates is to detect soft
X-ray emission from stellar astrospheres produced by charge exchange between
heavy ions of the stellar wind and cold neutrals of the interstellar medium
(ISM) surrounding the stars. Here we report detections of charge-exchange
induced X-ray emission from the extended astrospheres of three main sequence
stars, 70 Ophiuchi, epsilon Eridani, and 61 Cygni based on analysis of
observations by XMM-Newton. We estimate the corresponding mass loss rates to be
66.5 +- 11.1, 15.6 +- 4.4, and 9.6 +- 4.1 times the solar mass loss rate for 70
Ophiuchi, epsilon Eridani, and 61 Cygni, respectively, and compare our results
to the hydrogen wall method. We also place upper limits on the mass loss rates
of several other main sequence stars. This method has potential utility for
determining the mass loss rates from X-ray observations showing spatial
extension beyond a coronal point source.
