Observability of stellar winds from late-type dwarfs via charge exchange x-ray emission

Despite the fact that the overwhelming majority of stars are of late spectr al type (F-M) and lie on the main sequence, we know nothing about their ste llar winds. Existing measurements of winds only apply to high-mass O and B stars, red giants, and supergiants and only extend down to a few times 10(- 10) M. yr(-1), as compared to the solar rate of similar to2 x 10(-14) M. y( r-1). Attempts to detect winds from late-type dwarf stars have to date resu lted only in loose upper limits of order 10(-12) to 10(-11) M. yr(-1). We p ropose a novel method of studying stellar winds through observation of char ge exchange-induced X-ray emission. Recent X-ray detections of comets sugge st that charge transfer between highly charged ions in the solar wind and n eutral gases in cometary atmospheres is responsible for much or all of the observed emission, a hypothesis that has been strengthened by Chandra obser vations of comet C/1999 S4 (LINEAR). It has also been proposed that charge transfer between the solar wind and the local interstellar medium (ISM) pro duces a substantial fraction of the soft X-ray background observed by ROSAT and various rocket experiments. We show that the same process may be obser vable in nearby dwarf star systems using Chandra and future large-area high -resolution observatories, which would provide hitherto unobtainable inform ation on wind geometry, ion composition, mass-loss rates, and the distribut ion of neutral gas in the ISM.