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Astron. Astrophys. 362, 223-235 (2000)

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Time series analysis of V815 Herculis photometry between 1984 and 1998 *

L. Jetsu 1, T. Hackman 1, D.S. Hall 2, G.W. Henry 3, M. Kokko 1 and J. You 4

1 Observatory, P.O. Box 14, 00014 University of Helsinki, Finland
2 Dyer Observatory, Vanderbilt University, Nashville, TN 37235, USA
3 Center of Excellence in Information Systems, Tennessee State University, 330 10th Ave. North, Nashville, TN 37203-3401, USA
4 Astronomy Division, P.O. Box 3000, 90014 University of Oulu, Finland

Received 17 December 1999 / Accepted 14 August 2000

Abstract

As a case study of the solar-stellar connection, we have analysed a prolonged time series of BV photometry of the chromospherically active binary V815 Her. The surface differential rotation in the rapidly rotating G5v primary caused changes of 4.6% in the seasonal photometric rotation periods. This would imply a differential rotation coefficient of [FORMULA], if the rotation of the starspots follows the solar law of differential rotation and the activity is confined within the same latitudinal range as in the Sun, having [FORMULA] and the spectral-type of G2v. Our analysis of the primary and secondary minima of the seasonal light curves indicated that the regions of stronger activity have concentrated on one active longitude, which has maintained a constant rotation period of [FORMULA] for about 14 years. No regular activity cycle was detected in the mean brightness changes of V815 Her.

Key words: stars: individual: V815 Her – stars: variables: general – stars: activity – techniques: photometric

* Table 1 is available only in electronic form at CDS via anonymous ftp to ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+A/362/223 (130.79.1285) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/362/223 . These data are also available at http://schwab.tsuniv.edu/t3/v815her/v815her.html

Send offprint requests to: L. Jetsu (Lauri.Jetsu@astro.helsinki.fi)

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© European Southern Observatory (ESO) 2000

Online publication: October 30, 19100
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