On the 2800 MgII radiation field in binary star envelopes

The problem of ionization for magnesium and radiation field in k and h MgII doublet in common envelopes - roundchroms - formed around the RS CVn type systems is examined. It is shown that: a) The roundchroms are completely opaque in the lines of k and h MgII doublet; b) F, G or K type cool stars as secondary in such binaries ensure the complete ionization of magnesium atoms within the whole volume of roundchrom; c) The density of k and h MgII doublet radiation field in the main volume of roundchrom is extremely high, on four-five orders of magnitude, than is derived for its outer boundary. These results have direct relation to the observed saddle-like and very broad shapes of k and h MgII emission lines in the spectrum of RS CVn type close binaries.