The Wilson-Bappu relation for RS CVn stars

We investigate the extent to which the Wilson-Bappu relationship holds for chromospherically active binaries using the Mg II h&k lines of 41 RS CVn st ars observed with IUE. The resulting fits are different from the relationsh ips obtained for single, less active stars. The parallax used were those fr om the HIPPARCOS catalogue, these give a much better correlation than the m agnitudes taken from CABS. Within a particular luminosity class the relatio nship is good, however it tends to break down when we incorporate objects r anging in luminosity from class I to v. From model calculations there is ve ry little dependence of the Mg II line width on effective temperature. The line width does however depend on the column mass at the transition region boundary showing increased line width at lower column mass. There is also a dependence on the column mass adopted for the temperature minimum, however , the major and dominant parameter is the surface gravity scaling as g(-1/4 ). Within a luminosity class more active objects will show larger lines wid ths reflecting a higher column mass deeper in the atmosphere, e.g. at the t emperature minimum level.