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A spectroscopic study of RCB stars in the Galaxy and the LMC

Published online by Cambridge University Press:  15 February 2018

Karen Pollard ,
P.L. Cottrell  and
W.A. Lawson
Karen Pollard
Affiliation:
Mount John University Observatory, Department of Physics and Astronomy, University of Canterbury, Christchurch, New Zealand
P.L. Cottrell
Affiliation:
Mount John University Observatory, Department of Physics and Astronomy, University of Canterbury, Christchurch, New Zealand
W.A. Lawson
Affiliation:
, Department of Physics, University College ADFA, University of New South Wales, Canberra ACT 2600, Australia

Abstract

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High resolution échelle spectra have been obtained of two Large Magellanic Cloud (LMC) and one galactic R Coronae Borealis (RCB) star with the Anglo-Australian Telescope. An analysis of these data using He- and C-rich models and the model atmosphere code WIDTH6 of Kurucz indicates that the galactic RCB star SU Tau and the two LMC stars, W Men and HV12842, have similar atmospheric parameters to the warmer galactic RCB and hydrogen-deficient Carbon (HdC) stars e.g., R CrB and XX Cam. Specifically, the new stars have Teff ∼7000 K, log g = 0.5-1.0, microturbulent velocities between 6 and 8 km.s-1 and C/He ratios from 0.004 to 0.006.

An abundance analysis has been performed on these stars for a wide range of species. Special emphasis has been placed on particular elements H, He, Li, C, N, O, & Fe (see figure 1), which are key indicators of the extent and relative importance of nuclear processes such as the CNO cycle and triple-alpha process, and also of the physical processes such as convective mixing and mass loss. Specific values for the abundances of [H/He], [Li/Fe] and [Fe/total] (expressed relative to the total abundance of all species) in SU Tau and HV12842 are -5.4 & -6.4, +2.5 & +2.4, -0.4 & -0.8.

Type
Beyond the Classical Instability Strip
Information
International Astronomical Union Colloquium , Volume 139: New Perspectives on Stellar Pulsation and Pulsating Variable Stars , 1993 , pp. 215
Copyright
Copyright © Cambridge University Press 1993