A spectroscopic and photometric study of FK Comae in 1989

FK Comae is probably a recently coalesced binary system, since it is a G-type giant rotating near breakup yet has no detected orbital motion. To better understand its characteristics, which include extreme atmospheric activity and rapid variability, an intensive spectroscopic campaign was undertaken. Fifty-one CCD-echelle spectra of this atmospherically active, rapidly rotating single giant were obtained over a period of eight nights in the spring of 1989. Visual photometry and seven IUE spectra were acquired contemporaneously. The photometry showed smooth quasi-sinusoidal modulation with an amplitude of about 0.1 mag. Absorption and emission lines showed complicated but systematic behavior. Photospheric absorption lines were distorted by a Doppler-shifted bump caused by dark starspots resulting in small apparent radial velocity variations. No radial velocity variations characteristic of orbital motion were seen to a level of 3 km s^-1. Broad emission in Hα was modulated at the photospheric rotational amplitude, implying an origin no farther from the rotational axis than 1 stellar radius. Strong absorption appears within the Balmer emission as the starspot crosses the disk. The strengths of Ca II lines are modulated in phase with Hα but do not have velocity-modulated wings like Hα. He I D3 showed very complex and interesting behavior. It had an absorption core, emission wings, and modulation with more structure than the Balmer lines. It is probably responding to the coronal X-ray flux geometric distribution. While time coverage is not as good for the UV lines, Mg II correlates well with Hα but the higher temperature lines do not.