VARIATIONS OF BETA-COMAE THROUGH A MAGNETIC MINIMUM

The dwarf star beta Com = HR 4983 = HD 114710 (G0 V, B-V = 0.57) is cl ose to the Sun in the H-R diagram, being only approximate to 260 K hot ter. We present measurements done over several years of (1) the line d epth ratios of V I lambda 6251.83 to Fe I lambda 6252.57 to establish the temperature, (2) the line bisectors as a measure of the star's gra nulation, (3) Ca II H and K emission as an indirect indicator of magne tic activity, and (4) the blue and visual magnitudes as an indication of the power output. All these parameters show a similar variation con sisting of a broad minimum extending over approximately 5 years, but t he minima do not occur at the same epoch. The magnetic signature leads the others in time. Time lags relative to the magnetic variation are 0.9 +/- 0.3 yr for the photometric data, 2.9 +/- 0.3 yr for the temper ature, and 2.9 +/- 0.5 yr for the granulation. A 1% variation in radiu s during the 5 yr interval is indicated.