Astronomy Astrophysics Study of FK Comae Berenices

Abstract. We present 8 years of previously unpublished photometric observations of FK Com together with the determination of the stability of the primary comparison star HD 117567. The observations have been carried out between 1993 and 2001 at four dierent observatories and they consist of 5157 data points in total: U(903), B(994), V (1643), R(166), Ic(573), b(461) and y(417). We also analyse this new data together with the previously published photometric observations. The V magnitude shows variations with dominant periods of about 3, 6, 12, 14 and 31 years. The short-term light curve variations appear to be caused by rearrangement of approximately constant amount of cool spots. From the values for dierent colours obtained during the brightest season observed, corresponding to the supposedly unspotted surface, the spectral type of FK Com is determined to be G7 III