V453 Oph: a s-process enriched, but carbon-deficient RV Tauri star of low intrinsic metallicity

¹ Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium e-mail: Pieter.Deroo@ster.kuleuven.be
² Institut d'Astronomie et d'Astrophysique, Université Libre de Bruxelles, CP 226, 1050 Brussels, Belgium

Received: 18 August 2004
Accepted: 1 April 2005

Abstract

This paper reports the detection of a heavy element enriched RV Tauri variable with an abundance pattern that differs significantly from a standard s-process enriched object: V453 Oph. Based on optical high-resolution spectra, we determined that this object of low intrinsic metallicity () has a mild, but significant, enrichment () of heavy elements for which the distribution points to slow neutron capture nucleosynthesis. This result is strengthened by a comparative analysis to the non-enriched RV Tauri star DS Aqr (). Although V453 Oph is the first RV Tauri star showing a strong s-process signature, it is not accompanied by C enhancement, challenging our current nucleosynthetic models of post-AGB stars that predict a simultaneous enrichment in C and s-process elements. The low N abundance excludes CN cycling as being responsible for the low C abundance. We explore three different scenarios to explain the heavy element distribution in this evolved object: an enrichment of the parental cloud, an accretion scenario in which the chemical patterns were acquired by mass transfer in a binary system and an intrinsic enrichment by dredge-up.