The Wilson-Bappu Relation for RS CVn Stars F.F..pdf

AA manuscript no.(will be inserted by hand later)Your thesaurus codes are:02.12.1; 02.12.2; 08.01.2; 08.03.3; 08.12.1 ASTRONOMYANDASTROPHYSICSAugust 23, 1999The Wilson-Bappu Relation for RS CVn StarsF.F. Ozeren1;2, J.G. Doyle1 and D. Jevremovic1;31 Armagh Observatory, College Hill, Armagh BT61 9DG, N. Irelandemails: jgd@star.arm.ac.uk2 Dept. of Astronomy, Science Faculty of Ankara University, 06100 Tando~gan-Ankara/Turkeyemail: ferhat@astro1.science.ankara.edu.tr3 Belgrade Observatory, Volgina 7, 11000 Belgrade, Yugoslaviaemail: darko@aob.aob.bg.ac.yuthe date of receipt and acceptance should be inserted laterAbstract. We investigate the extent to which theWilson-Bappu relationship holds for chromosphericallyactive binaries using the Mg ii hk lines of 41 RS CVnstars observed with IUE. The resulting ts are dierentfrom the relationships obtained for single, less active stars.The parallax used were those from the hipparcos cata-logue, these give a much better correlation than the mag-nitudes taken from CABS. Within a particular luminosityclass the relationship is good, however it tends to breakdown when we incorporate objects ranging in luminosityfrom class i to v. Frommodel calculations there is very lit-tle dependence of the Mg ii line width on eective temper-ature. The line width does however depend on the columnmass at the transition region boundary showing increasedline width at lower column mass. There is also a depen-dence on the column mass adopted for the temperatureminimum, however, the major and dominant parameter isthe surface gravity scaling as g1=4. Within a luminosityclass more active objects will show larger lines widths re- ecting a higher column mass deeper in the atmosphere,e.g. at the temperature minimum level.Key words: Wilson-Bappu eect | Mg ii hk lines |stellar chromospheres | column mass1. IntroductionThe Wilson-Bappu relationship (hereafter the WB rela-tionship) was rst established as a relation between theabsolute visual magnitude (Mv) a