BVR photometry and H spectroscopy of RS CVn type binary MM Herculis^*

¹ Ege University Observatory, Bornova, İzmir, Turkey e-mail: tas, sevren, ibanoglu@astronomy.sci.ege.edu.tr
² Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy e-mail: gma@sunct.ct.astro.it; afr@sunct.ct.astro.it; scat@sunct.ct.astro.it

Corresponding author: S. Evren, sevren@astronomy.sci.ege.edu.tr

Received: 3 April 2001
Accepted: 26 June 2001

Abstract

The RS CVn type eclipsing binary MM Herculis was observed photo-electrically using B, V and R filters in 1998 and 1999 and the light and colour curves were obtained. Spectroscopic observations were carried out in 1999. The new light and colour curves are anti-correlated with the observations of 1997, i.e. the system is bluer when it is faintest. The variations of the brightnesses at each special phase (0.0, 0.25, 0.5, and 0.75) show an almost cyclic change with a period of about 6 years. This value is in good agreement with the migration periods of the spots suggested by us previously. The outside-of-eclipse wave in the light curve shows a minimum at phase ≈0.50, and the mean colour of the system is the bluest at the same phase. When the spots located on the cooler component are seen around phase 0.50, the amplitude of the light variation outside eclipse is larger than the others. Such variation may be caused by the effect of the hotter component. Spectroscopic observations of the system were carried out in the spectral range 5860-6700 Å. The subtraction of a "synthetic" spectrum, built up with spectra of inactive standard stars, allows us to detect an Hα emission excess only from the cool component. New radial velocity measurements of the system were obtained and analyzed for the orbital parameters.