Magnetic, Photometric, Temperature, and Granulation Variations of XI Bootis A 1984--1993

The magnetically active G8 dwarf star, ξ Boo A = HR 5544 = HD 13 1156 is studied for magnetic- cycle type variations over the 1984-1993 interval. We present measurements of Ca II H and K emission as an indirect indicator of magnetic activity, blue and visual magnitudes as an indication of the power output and temperature, line-depth ratios of V I λ6251.83 to Fe I λ6252.57 as a measure of temperature, and line bisectors as a measure of the star's granulation. The season means of all these parameters show the same pattern of variation with several irregular rises and falls, rather different from the relatively smooth variations seen for the Sun. As found for several other stars in previous studies, the magnetic signal leads the others in time. Time lags relative to the H and K index variation are 1.4±0.4 yr for the photometric brightness, 1.5±0.5 yr for the b -y color index, 1.8±0.3 yr for the line-depth ratio, and 2.1±0.4 yr for the line bisectors. The ≈1.7 year temperature lag for ξ Boo A is close to the linear relation between lag and effective temperature found for the other stars that have been measured.