Webo 1: a Young Barium Star Surrounded by a Ring-like Planetary Nebula

WeBo 1 (PN G135.6+01.0), a previously unrecognized planetary nebula with a remarkable thinring morphology, was discovered serendipitously on Digitized Sky Survey images. The central star is found to be a late-type giant with overabundances of carbon and s-process elements. The giant is chromospherically active and photometrically variable, with a probable period of 4.7 days; this suggests that the star is spotted, and that 4.7 days is its rotation period. We propose a scenario in which one component of a binary system became an AGB star with a dense stellar wind enriched in C and sprocess elements; a portion of the wind was accreted by the companion, contaminating its atmosphere and spinning up its rotation. The AGB star has now become a hot subdwarf, leaving the optical companion as a freshly contaminated barium star inside an ionized planetary nebula. Subject headings: binaries: close — nuclear reactions, nucleosynthesis, abundances — planetary nebulae: individual (WeBo 1) — stars: AGB and post-AGB — stars: chemically peculiar — stars: carbon