SILICON ABUNDANCES IN POPULATION-I GIANTS

Silicon to carbon abundance ratios for Population I giants were determ ined from emission lines originating in the transition layers between stellar chromospheres and coronae. For effective temperatures larger t han 6200 K we find a group of stars for which the silicon to carbon ab undance ratio appears to be increased. These stars are presumably desc endents from Ap stars on Am stars with increased surface silicon to ca rbon abundance ratios. Around B - V almost-equal-to 0.45 this anomaly disappears as is to be expected due to the increased depth of the conv ection zone and therefore deeper mixing which dilutes the surface over abundances. Unexplained is the apparent increased silicon to carbon ab undance ratio observed for several stars cooler than 5100 K. RS CVn an d related stars do not show this increased abundance ratio.