SALT reveals the barium central star of the planetary nebula Hen 2-39

Abstract

Classical barium stars are binary systems which consist of a late-type giant enriched in carbon and slow neutron capture (s-process) elements and an evolved white dwarf (WD) that is invisible at optical wavelengths. The youngest observed barium stars are surrounded by planetary nebulae (PNe), ejected soon after the wind accretion of polluted material when the WD was in its preceeding asymptotic giant branch (AGB) phase. Such systems are rare but powerful laboratories for studying AGB nucleosynthesis as we can measure the chemical abundances of both the polluted star and the nebula ejected by the polluter. Here we present evidence for a barium star in the PN Hen 2-39. The polluted giant is very similar to that found in WeBo 1. It is a cool (Teff=4250 +/- 150 K) giant enhanced in carbon ([C/H]=0.42 +/- 0.02 dex) and barium ([Ba/Fe]=1.50 +/- 0.25 dex). A spectral type of C-R3 C_24 nominally places Hen 2-39 amongst the peculiar early R-type carbon stars, however the barium enhancement and likely binary status mean that it is more likely to be a barium star with similar properties, rather than a true member of this class. An AGB star model of initial mass 1.8 Msun and a relatively large carbon pocket size can reproduce the observed abundances well, provided mass is transferred in a highly conservative way from the AGB star to the polluted star (e.g. wind Roche-lobe overflow). The nebula exhibits an apparent ring morphology in keeping with the other PNe around barium stars (WeBo 1 and A 70) and shows a high degree of ionization implying the presence of an invisible hot pre-WD companion that will require confirmation with UV observations. In contrast to A 70, the nebular chemical abundance pattern is consistent with non-Type I PNe, in keeping with the trend found from nebular s-process studies that non-Type I PNe are more likely to be s-process enhanced. (abridged)

Accepted for publication in MNRAS. 15 pages, 8 figures and 8 tables

References in corpus (12)

• The initial-final mass relationship of white dwarfs revisited: effect on the luminosity function and mass distribution
• First science with SALT: peering at the accreting polar caps of the eclipsing polar SDSS J015543.40+002807.2
• The Magellanic Cloud Calibration of the Galactic Planetary Nebula Distance Scale
• Nucleosynthesis Predictions for Intermediate-Mass AGB Stars: Comparison to Observations of Type I Planetary Nebulae
• Chemical abundances for Hf 2-2, a planetary nebula with the strongest known heavy element recombination lines
• He~I Emission in the Orion Nebula and Implications for Primordial Helium Abundance
• Chemical compositions and plasma parameters of planetary nebulae with Wolf-Rayet and wels type central stars
• Origin of the early-type R stars: a binary-merger solution to a century-old problem?
• White-dwarf red-giant mergers, early-type R stars, J stars and lithium
• The s-process in stellar population synthesis: a new approach to understanding AGB stars
• Stellar population synthesis of post-AGB stars: the s-process in MACHO47.2496.8
• A Small Step on the Long Road to Understanding the R-Stars: CNO Cycling in Candidate R-Star Progenitors

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