Stringent X-ray constraints on mass loss from Proxima Centauri

We have analyzed data from two Chandra imaging observations of Proxima Centauri, searching for an Xray halo arising from charge exchange between highly charged ions in its stellar wind and neutral gas in the surrounding interstellar medium. Based upon our model of Proxima Cen's charge exchange emission, the absence of any detectable charge exchange signal places a statistical 3 upper limit of similar to3 x 10(13) M. yr(-1) (14 (M) over dot .) on the mass-loss rate (9 (M) over dot . for the 2 sigma limit and 4 (M) over dot . for 1 sigma), with a model uncertainty of roughly a factor of 3. This is orders of magnitude smaller than the upper limits that have been placed on late-type dwarf stars using radio observations, and it supports a recent mass-loss result for Proxima Cen based on Lyalpha absorption profiles. We have also studied the coronal spectrum, both in quiescence and during a prominent flare. Results are consistent with those obtained in previous X-ray observations, but a firm determination of coronal metal abundances remains elusive.