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Keywords:

  • binaries: eclipsing;
  • stars: activity;
  • stars: individual (MM Her);
  • stars: late-type;
  • starspots;
  • techniques: photometric

Abstract

We present the long-term multi-colour photometry of MM Her which is one of the first members of the RS CVn-type of eclipsing binary systems. We took advantage of its photometry-spanning 33 years to evaluate its long-term variation, which is caused by the evolution of the activity structures located on the surface of the cooler component. In this study we found that the long-term variation in the brightness, colour, and amplitude of seasonal light curves over the years could be represented by two periods: one of which is of around 22.5 years, and is similar to all in this regard, but the other is a period value of about 9.5 years for the brightness variation, and of about 7.5 years for the variation in colour and amplitude. The analysis of the spot minimum phases gives a migration period of approximately 7.8 years. We also presented a new light curve analysis solution, and improved its light elements in this study. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)