Astron. Astrophys. 349, 546-552 (1999)

The activity pattern on MM Herculis: spots and faculae

G. Tas, S. Evren and C. Ibanoglu

Ege University Observatory, Bornova, Izmir, Turkey (tas, sevren, ibanoglu@alpha.sci.ege.edu.tr)

Received 5 January 1999 / Accepted 26 May 1999

Abstract

The RS CVn type eclipsing binary MM Herculis was observed using B, V, and R filters in 1997 and the light and colour curves were obtained. The long-term (1976-1997) variations in the brightness and colour of the system were revealed by examining 12 light and colour curves. The reason for the variations in the B-V colour curves may be the photospheric bright facular structures that surround starspots. The system is bluest when at its faintest. Migration periods of 5.8 and 5.9 years have been found for the two spots or spot groups, which are located on the cooler component. The spots that are located within the longitude difference of 180^o seem to approach each other with a period of six years. In this case the amplitudes of the light curves increase, the system's mean brightness decreases and its mean colour becomes bluer.

Key words: stars: activity stars: individual: MM Her stars: late-type stars: starspots

Send offprint requests to: S. Evren (sevren@alpha.sci.ege.edu.tr)

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Contents

• 1. Introduction
• 2. Observations
• 3. Photometric variations
  • 3.1. The light and colour curves (1976-1985)
  • 3.2. The migration period
  • 3.3. Distribution of the spots and their effects
• 4. Results and discussion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: September 2, 1999
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