STELLAR CORONAE AT THE END OF THE MAIN-SEQUENCE - A ROSAT SURVEY OF THE LATE M-DWARFS

We present X-ray data, both detections and upper limits, from the ROSA T all-sky survey for most known M dwarfs later than type M5, as well a s from selected ROSAT pointed observations of some of these stars. We compare these data with similar data for early M dwarfs in an attempt to probe the nature of the magnetic dynamo and coronal heating mechani sm for the very late M dwarfs, which are presumably totally convective . Our results indicate that late M dwarfs can have coronae which are j ust as active as those for the early M dwarfs and that coronal heating efficiency for ''saturated'' stars (as evidenced from L(X)/L(bol)) do es not drop at spectral type M6.