The nature of magnetic activity at the low-mass end of the main-sequence

We propose a systematic investigation of magnetic activity on ultracool dwarfsat the spectral type M/L transition. XMMNewton allows to trace the effects ofboth nonthermal and thermal processes in cool star atmospheres simultaneously,using EPIC to detect coronal Xrays and the Optical Monitor to record opticalemission in response to nonthermal electrons. We selected a sample of nearbyultracool dwarfs known to maintain magnetic fields and mostly yielding evidencefor chromospheres. We aim at constraining the nature and efficiency of stellardynamos and coronal heating at the bottom of the mainsequence by searching forthe quiescent corona, establishing flare energy distributions, and studying theconnection between chromospheric and coronal activity indicators. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]