1997A&A...321..811O

We present a spot modeling analysis of the active late-type giant HK Lac using 30 years of photometry, including 600 new data points from the last six years. We have analyzed folded light curves and, when we had long continuous data sets, applied a new computer code for time-series modeling. The validity of the modeling results was tested as a function of the photometric noise. We have determined the unspotted brightness of HK Lac in the BV(RI)_C bandpasses and obtained a spot temperature of {DELTA}T=1200±100K. Polar active regions were recovered throughout the modeling because no other scenario was able to describe both the mean light variability of over 0.25mag accompanied by rotational modulation of similar amplitude. This result has gotten strong theoretical support recently (see Schuessler). The active regions preferably cluster around two orbital phases separated by ≃110°. New spot appearences within active regions and, possibly, their interactions with the old ones could be the cause of rapid changes in the light curves.