MAGNETIC, PHOTOMETRIC, TEMPERATURE, AND GRANULATION VARIATIONS OF XI-BOOTIS-A 1984-1993

The magnetically active G8 dwarf star, xi Boo A = HR 5544 = HD 131156 is studied for magnetic-cycle type variations over the 1984-1993 inter val. We present measurements of Ca II H and K emission as an indirect indicator of magnetic activity, blue and visual magnitudes as an indic ation of the power output and temperature, line-depth ratios of V I la mbda 6251.83 to Fe I lambda 6252.57 as a measure of temperature, and l ine bisectors as a measure of the star's granulation. The season means of all these parameters show the same pattern of variation with sever al irregular rises and falls, rather different from the relatively smo oth variations seen for the Sun. As found for several other stars in p revious studies, the magnetic signal leads the others in time. Time la gs 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 b isectors. The approximate to 1.7 year temperature lag for xi Boo A is close to the linear relation between lag and effective temperature fou nd for the other stars that have been measured.