Transition Region Emission From Very Low Mass Stars

Abstract

We present results from our cycle 10 HST program to search for transition region emission in very low-mass, main-sequence stars in the spectral range M7-M9. Our program is aimed at 1) detecting emission; and 2) distinguishing between flaring and quiescent origin for the emission. We have obtained HST/STIS time series observations of three active, very low mass stars (VB 8, VB 10, and LHS 2065) which show persistent activity in transition region lines including Si IV, C IV, He II. Emission in transition region lines appears to be variable between exposures, but is always observed. A strong flare was also observed in one 10 minute exposure on VB 10. Our results indicate that active, very low-mass stars maintain a persistent quiescent chromosphere and transition region that is similar to those observed in active, earlier type M dwarfs, in contrast to suggestions that these low-mass, main-sequence stars exhibit only relatively strong flares and no quiescent emission.