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Astron. Astrophys. 321, 811-821 (1997)

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Time-series photometric spot modeling

III. Thirty years in the life of HK Lacertae

K. Oláh 1, Zs. Kvári 1, J. Bartus 1, 2, K.G. Strassmeier 2, D.S. Hall 3 and G.W. Henry 4

1 Konkoly Observatory of the Hungarian Academy of Sciences, H-1525 Budapest, Hungary (olah@ogyalla.konkoly.hu, kovari@buda.konkoly.hu, bartus@buda.konkoly.hu)
2 Institut für Astronomie, Universität Wien, Türkenschanzstraße 17, A-1180 Wien, Austria (strassmeier@astro.ast.univie.ac.at)
3 Dyer Observatory, Vanderbilt University, Nashville, TN 37235, USA (hallxxds@ctrvax.vanderbilt.edu)
4 Center for Automated Space Science and Center of Excellence in Information Systems, Tennessee State University, Nashville, TN 37203-3401, USA (henry@coe.tnstate.edu)

Received 2 September 1996 / Accepted 5 November 1996


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 [FORMULA] bandpasses and obtained a spot temperature of [FORMULA]  K. Polar active regions were recovered throughout the modeling because no other scenario was able to describe both the mean light variability of over [FORMULA] accompanied by rotational modulation of similar amplitude. This result has gotten strong theoretical support recently (see Schüssler 1996). The active regions preferably cluster around two orbital phases separated by [FORMULA]. 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.

Key words: stars: activity – stars: late-type – stars: individual: HK Lac – stars: spots

Send offprint requests to: K. Oláh

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998