Stellar magnetic fields: From the photosphere into the corona

Simultaneous Xray and optical observations of the active M dwarf CN Leo haveshown variability in its magnetic flux (as measured through magneticallysensitive lines in the molecular FeH band) on different timescales: within a fewdays, within one night, and possibly even related to a flare event. We proposeto extend these studies to a larger sample of stars and observe the two flarestars Proxima Cen and YZ CMi simultaneously with XMMNewton and VLT/UVES inorder to characterize the amplitudes and time scales of variations in theirphotospheric magnetic fields together with the behavior of chromosphericemission lines and coronal Xray emission. This will enable us to traceactivityrelated changes in the stellar magnetic field through all layers of the stellar atmosphere. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]