Independence of Chromospheric Activity and Soft X-Ray Flaring on the Flare Star EV Lacertae

EXOSAT observed the flare star EV Lacertae for 17 hr over 2 days in October 1985. Two flaring episodes were recorded. During a significant fraction of these observations, IUE, photometric and spectroscopic coverage was available. A 2-hour long period of X-ray flaring was observed during which there was no U-band activity and almost no chromospheric activity. On the other hand, two ΔU ~ 1° m° 5 optical flares produced normal chromospheric enhancements, but only a weak X-ray response. We suggest that these and a few other observations of stellar flares may imply the occasional existence of magnetically isolated regions in M-dwarf atmospheres.