1 Introduction

The RS CVn-type eclipsing binary MM Her (BD $+22\hbox{$^\circ$ }\,3245$, G2V+K0IV, $V_{\rm max}=9\hbox{$.\!\!^{\rm m}$ }5, P_{\rm orb}= 7\hbox{$.\!\!^{\rm d}$ }96)$ was first observed visually by Tsesevich (1954) and, later, its light variations were discussed by many different authors (e.g. Sowell et al. 1983; Evren 1985, 1987a, 1987b; Heckert & Ordway 1995; Evren & Tas 1999; Tas et al. 1999). MM Her shows an outside-of-eclipse wave-like distortion which is one of the main characteristics for RS CVn-type binaries. The migration period of the wave-like distortion was calculated by different investigators to be between 3 and 8 years. Tas et al. (1999) (hereafter Paper I) have given two migration periods by considering the effect of two spots with a period of about 6 years. They also showed that the light (in V) and colour (in B-V) curves vary in anti-correlation. In general, the light and colour variations occur at the same phase in binaries of these type, and the active star is redder when it is at the minimum light, in agreement with the hypothesis of cool starspots as the cause of light variation. Conversely, in the case of MM Her, at the minimum light the colour of the system is bluer. Therefore, we proposed that the blueing in B-V colour may arise from the photospheric bright facular structures that surround starspots. Evidence of B-V and, more strongly, U-B color curves correlated with the V light curve have been provided for other very active systems, like UX Ari and HR 1099 (see e.g. Catalano et al. 1996). U excess in active systems correlated with the activity level has been discussed by Amado & Byrne (1997) and ascribed to faculae prominent in the near-UV continuum. Recently, the new BVR light curves obtained from photoelectric observations made in 1998 and 1999 were published by Tas (2000a).

MM Her has also been studied spectroscopically by Imbert (1971), Popper (1988) and Hall & Ramsey (1992), and they found the $\gamma$ velocity as -50.8 kms^-1, -51.5 kms^-1 and -54.2 kms^-1, respectively.

In this paper, we focus on the long-term photometric behaviour, cyclic variations in the brightnesses and new H$\alpha$ spectroscopy of the system. Section 2 summarizes the observations and calculations. In Sect. 3, we present some results which were obtained from the light curves and some evidence for the activity of the cooler component. Section 4 is devoted to the spectroscopic results. The variations of the equivalent width and the H$\alpha$ emission are discussed and a new radial velocity curve obtained and analyzed for the orbital parameters presented. The last section contains conclusions.