1 Introduction

Stars which are forced into rapid rotation through tidal interaction in binary systems exhibit high levels of activity. A large number of observations have demonstrated the fundamental importance of stellar rotation for the generated activity level. Studies which relate the characteristics of star activity to basic star parameters are a natural way to test dynamo theories.

The strong photospheric, chromospheric, transition region and coronal activity in RS CVn stars are generally attributed to the deep convection zone and the fast rotation that drives the dynamo mechanism. Enhanced emission cores in the CaII H and K as well as the H$_{\alpha }$ lines are the primary optical indicators of the chromospheric activity (Fernandez-Figueroa et al. 1994). Analysis of the spectra at different orbital phases allows us to establish which star is the source of the emission. If the activity of RS CVn stars is linked to the stellar dynamo then the short-period RS CVn stars have a proportionally larger supply of rotational energy to be converted into magnetic energy.

The eclipsing binary star SV Cam (G2-3V+K4V) belongs to the subgroup of short-period RS CVn systems and it is one of the closest binaries among them ( $P_{\rm orb}=0.6$ days) with an orbital inclination $i\geq80{\hbox{$^\circ$ }}$. The star shows remarkable changes out of the eclipses. Variations of the light curve shape by as much as 0.1 mag on time scales as short as one month have been observed. Extensive observations from 1973 until 1980 led Patkos (1982a,b) to the conclusion that cool spots on the surface of the primary component and sporadic gas streams are present in the system. Hempelmann et al. (1997) found evidence for chromospheric activity of the secondary star of SV Cam by an analysis of the strength of the H$_{\alpha }$ absorption line during the primary and secondary eclipses. SV Cam does not show all of the signatures of RS CVn-type activity: there is no apparent H$_{\alpha }$ emission, neither radio emission nor flare activity have been reported.

Results from X-ray observations of SV Cam are contradictory. Agrawal et al. (1980) and Welty $\&$ Ramsey (1995) reported high X-ray luminosity and surprisingly large X-ray surface flux compared to that observed in semi-detached, Algol-type systems (Singh et al. 1980). On the other hand, Hempelmann et al. (1997) found the total X-ray output from SV Cam to be on a level typical of single Main Sequence stars, i.e. the observed coronal activity of this system is not enhanced compared to single stars. In semi-detached systems the mass transfer through the inner Lagrangian point is responsible for the higher X-ray flux. In case of SV Cas, however, due to its low Roche lobe filling factor this explanation is not valid. Hempelmann et al. (1997) modelled the X-ray light curve of SV Cam with two localized coronal emission regions rather than by global emission coming either from a homogeneously radiating stellar corona or from a common envelope surrounding the two stars. Although SV Cam is photometrically a well-studied star, only the primary's radial velocity curve was known until Pojmanski (1998), thus making any inferences from analysis of the data unreliable.

In order to search for a presence of the secondary star's lines in the spectrum of SV Cam and to investigate the phase behavior of the H$_{\alpha }$ line which is a spectroscopic indicator of stellar chromospheric activity (Zarro $\&$ Rogers 1983; Herbig 1985; Frasca $\&$Catalano 1994; Strassmeier et al. 1990), we decided to observe SV Cam in the spectral range around this line. An additional reason for undertaking these spectral observations was to compare the derived star parameters with those obtained from the light curve modeling. The multicolor light curve of SV Cam in 1997 was modeled with two circular cool spots having an angular size of 20 ${\hbox{$^\circ$ }}$ located in the middle latitudes above and below the star equator, on opposite hemispheres of the primary star surface (Kjurkchieva et al. 2000a, hereafter Paper I).

Spectroscopic observations are described in the next section. In Sect. 3 we present the new radial velocity solution. The evidence of the enhanced H$_{\alpha }$ emission of the secondary star is shown by an analysis of the line profiles in the middle of the primary eclipse. In Sect. 4 we discuss our spectral data in the framework of the dynamo theory of stellar activity and show a good agreement of the values of the parameters of stars determined both from our spectral and photometric data.