16487

We recently published evidence for a steep decline in chromospheric ultraviolet emission compared with coronal X-ray emission for mid-to-late M dwarfs. Very late M dwarfs appear to be underluminous in the ultraviolet by two orders of magnitude. If confirmed comma this chromospheric decline will have profound implications for the habitability of exoplanet systems similar to TRAPPIST-1. The chromospheric decline may also point to a change in stellar dynamo mechanism at the fully convective boundary. We propose XMM-Newton and HST observations of three very late M dwarfs in order to test that the chromospheric decline is a common feature of the class.