Photospheric Spots and Flare on the Active Dwarf Star FR Cnc

We perform analysis of new BVRI photometry of young active dwarf star FR Cnc (K7V), obtained at Kourovka astronomical observatory of Ural Federal University with the help of multichannel electrophotometer in February 2010. The lightcurve displays sinusoidal rotation modulation with the amplitude of 0 m .15 in V band. Reddening of the brightness at the photometric minimum confirms that this modulation is caused by cold photospheric spots. An analysis of the spottedness distribution in terms of a zonal model based on our own and published data shows that the spots are localized at lower and middle latitudes from 47° to 56°, occupy 10-21% of the star’s area, and are colder than the photosphere by 1650 K. A flare was detected on February 3, 2010, at a time corresponding to HJD=2455231. 3136. A maximum amplitude of 0 m .11 was observed in the B band, the amplitudes in the V , R , and I bands were 0 m .04, 0 m .03, and 0 m .02, respectively, and the duration of the flare was 32.5 min. It was noted that the flare occurred near the maximum spottedness of the star. The calculated total energy of the flare was 2.4·10 33 and 1.3·10 33 erg in the B and V bands, respectively. The flare was found to have an afterglow, with an overall increase in the star’s brightness by 0 m .02 in the B band after the flare compared to the pre-flare level.