AN ABUNDANCE ANALYSIS OF R-CORONAE-BOREALIS STARS IN THE GALAXY AND THE LMC

High-resolution echelle spectra have been obtained of one galactic and two Large Magellanic Cloud (LMC) R Coronae Borealis (RCB) stars with the Anglo-Australian Telescope. An analysis of these data using He- an d C-rich models and the WIDTH6 model atmosphere code of Kurucz indicat es that the galactic RCB star SU Tau and the two LMC stars, HV 12842 a nd W Men (HV 966), have similar atmospheric parameters to the warmer g alactic RCB and hydrogen-deficient carbon (HdC) stars such as R CrB an d XX Cam. The newly analysed RCB stars have T(eff) approximately 7000 K, log g = 0.5 to 1.0, microturbulent velocities between 7 and 8 km s- 1 and C/He ratios ranging from 0.0034 to 0.011. An abundance analysis has been performed on these stars for a wide range of species. Special emphasis has been placed on H, He, Li, C, N, O, Fe and the s-process elements. Specific values for [H/He], [Li/Fe] and [Fe/total] (expresse d relative to the total abundance of all species) in SU Tau, HV 12842 and W Men are -5.4, -6.2 and -6.5; +2.6, +2.4 and +2.1; and -0.4, -0.7 and -0.7 respectively. The analysis of RCB stars in the LMC provides us with the opportunity to study the metallicity dependence of RCB sta r evolution.