Starspots and the rotation of the flare star EV Lac

Sinusoidal variations in the magnitude of EV Lac outside of flares are interpreted as due to intensity modulations from a photospheric spot group. No variations are detected in the color indices. An upper limit set by observational uncertainties indicates that the temperature difference between the photosphere and the spot region is only a few hundred degrees. The period of the cyclic magnitude variations is determined for the first time for EV Lac, and my best estimate is P=4.378 days. This implies an equatorial rotational velocity of 4.2 +- 0.5 km s-1. The equivalent width of the Hβ emission line does not vary, as measured through a set of interference filters. A larger scatter is evident in the measurements of the Hα emission, however, but the variations in this line do not correlate clearly with the rotation of EV Lac. The variation in the equivalent width of the Hα line is about one hundred percent. We are led to the conclusion that the prominent emission seen in the Hα line is formed partly in the chromosphere of EV Lac and partly in flare-associated regions of the atmosphere, and with a possible contribution also from analogs to solar plage areas