THE X-RAY VIEW OF THE LOW-MASS STARS IN THE SOLAR NEIGHBORHOOD

We present the results of a complete and sensitive X-ray survey of all known stars of spectral type K and M in the immediate solar vicinity with distances less than 7 pc. The X-ray data were obtained primarily from the ROSAT ail-sky survey (RASS); those program stars not detected in the RASS data were subsequently studied with the ROSAT pointed observation program. These new X-ray observations resulted in a detection rate of almost 94% for all K and M stars within 6 pc around the Sun, and 87% for K and M dwarfs within 7 pc around the Sun, The resulting X-ray luminosity distribution function can be well described by a log-normal distribution; the largest and smallest X-ray luminosities from our sample stars differ by almost four orders of magnitude. We show the existence of a correlation between total emitted X-ray luminosity and spectral hardness, such that more luminous objects tend to have larger spectral hardness, thus implying higher coronal temperatures. A comparison with Einstein data shows the lack of significant variability in excess of a factor of 2 in our sample stars.