Deviation from the Wilson-Bappu relationship in faint red dwarf stars.
Carlsson, M.; Engvold, O.; Elgaroy, O.
Norway
Abstract
New observations of the Mg II h and k lines on red dwarf stars have been carried out with the International Ultraviolet Explorer observatory. It is found that several of the dwarf stars in the sample have Mg II h and k lines which are narrower than expected from the Wilson-Bappu relationship, that is established for stars brighter than M(v) about 7. The deviations may depend on the Mg II h and k line opacity. Evidence is presented in favor of the suggestion that the optical thickness of the Mg II lines in faint red dwarfs depends on the level of activity of the stars. Calculations based on models for the sun and YZ CMi (Mv = 12.3) support the observational results.