TIME-SERIES PHOTOMETRIC SPOT MODELING .3. 30 YEARS IN THE LIFE OF HK LACERTAE

We present a spot modeling analysis of the active late-type giant HK L ac using 30 years of photometry, including 600 new data points from th e last six years. We have analyzed folded light curves and, when we ha d long continuous data sets, applied a new computer code for time-seri es modeling. The validity of the modeling results was tested as a func tion of the photometric noise. We have determined the unspotted bright ness of HK Lac in the BV(RI)(C) bandpasses and obtained a spot tempera ture of Delta T = 1200 +/- 100 K. Polar active regions were recovered throughout the modeling because no other scenario was able to describe both the mean light variability of over 0.(m)25 accompanied by rotati onal modulation of similar amplitude. This result has gotten strong th eoretical support recently (see Schussler 1996). The active regions pr eferably cluster around two orbital phases separated by approximate to 110 degrees. New spot appearances within active regions and, possibly , their interactions with the old ones could be the cause of rapid cha nges in the light curves.