Spectral activity of the Seyfert galaxy Markarian 6 in 1970-1991

We present results of the reduction of the archive spectra of the nucleus of Mrk 6 obtained in 1970-1991 using the image tube spectrograph at the 2.6-m Shajn telescope of the Crimean Astrophysical Observatory. We analyze 363 spectra for 181 dates obtained in the H (beta)spectral region. The spectra in the H (alpha)region (194 spectra for 179 dates) were used to get light curves. The light curves in the H (bea)and H (alpha)lines and also in the adjacent continuum show appreciable variability. Broad-line profile parameters (such as centroid, width, blue-to-red ratio of fluxes) seem to be independent of or dependent very weakly on the continuum flux. However, there is a tendency for the blue-to-red ratio of fluxes to increase with increasing continuum flux, and also a weak tendency for the profile width (profile dispersion) to decrease with increasing continuum flux. An anti-correlation between H (beta)shapes at the blue and red wings, positive correlation between blue shape and line/continuum flux, and anti-correlation between red shape and line/continuum flux show that the blue segments respond slightly better to the continuum changes than the red segment and total H (beta)line. We assume that the observed broad profile consists of at least two components with fixed profiles. We found that one of the components is nearly symmetric and has a single peak, while the other component has a blue bump and extended red wing. In terms of such a two-broad-components profile model, the evolution of the observed H (beta)profiles can be roughly reproduced by changes in the relative strength of the two variable components. However, the evolution of the broad H (beta) profile in Mrk 6 is complicated and not clear at all. The evolution is driven, most likely, by a set of various factor, including a multicomponent BLR model with redistribution of ionizing radiation between different parts of the BLR, the matter redistribution, reverberation effects, and continuum-dependent changes.