An abundance analysis of R Coronae Borealis stars in the Galaxy and the LMC

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Abstract
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- and C- rich models and the WIDTH6 model atmosphere code of Kurucz indicates that the galactic RCB star SU Tau and the two LMC stars, HV 12842 and W Men (HV 966), have similar atmospheric parameters to the warmer galactic RCB and hydrogen-deficient carbon (HdC) stars such as R CrB and XX Cam. The newly analysed RCB stars have |$T_{\rm eff} \sim 7000\, {\rm K}, \log g = 0.5 \ {\rm to} \ 1.0$|⁠, microturbulent velocities between 7 and |$8\ {\rm km \ s}^{-1}$| 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] (expressed 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 star evolution.

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