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Hydrogen deficient stars; irregular variables; abundances; evolution

This review presents a selection of recent highlights of observations of R Coronae Borealis variables. Emphasis is placed on an abundance analysis of a complete sample (18 stars) of the warm galactic RCBs. It is shown that 14 of the 18 have very similar compositions: the iron mass fraction ranges about a factor of 3 around the solar value (assuming C/He = 3%) but abundance ratios X/Fe for elements from Na to Ba show little variation. By contrast, the other 4 stars are deficient in iron but not in Na, Si, S and some other elements. With for example, [Si/Fe] ≃ 2, the quartet is indeed ‘peculiar’. One of the quartet, V854 Cen shows depletions of elements (other than CNO) similar to the depletions seen in interstellar medium corresponding to average logn(H_tot) = − 1.5. Scenarios for creating RCB from normal single and double stars are summarised.

David L. Lambert¹ N. Kameswara Rao²

1. Department of Astronomy, University of Texas, Austin, TX, USA
2. Indian Institute of Astrophysics, Bangalore - 560 034

Published

March 1994

Manuscript received

6 January 1994

Accepted

29 January 1994