4.6 Article

Binary evolution along the red giant branch with BINSTAR: The barium star perspective

期刊

ASTRONOMY & ASTROPHYSICS
卷 639, 期 -, 页码 -

出版社

EDP SCIENCES S A
DOI: 10.1051/0004-6361/202037487

关键词

binaries: spectroscopic; stars: late-type; stars: low-mass; stars: evolution

资金

  1. Fonds voor Wetenschappelijk Onderzoek Vlaanderen (FWO) [ZKD1501-00-W01]
  2. Belgian Science Policy Office [BR/143/A2/STARLAB]

向作者/读者索取更多资源

Barium (Ba), CH, and extrinsic or Tc-poor S-type stars are evolved low- and intermediate-mass stars that show enhancement of slow-neutron-capture-process elements on their surface, an indication of mass accretion from a former asymptotic giant branch companion, which is now a white dwarf (WD). Ba and CH stars can be found in the main-sequence (MS), the sub-giant, and the giant phase, while extrinsic S-type stars populate the giant branches only. As these polluted stars evolve, they might be involved in a second phase of interaction with their now white dwarf companion. In this paper, we consider systems composed of a main-sequence Ba star and a WD companion when the former evolves along the red giant branch (RGB). We want to determine if the orbital properties of the known population of Ba, CH, and S giants can be inferred from the evolution of their suspected dwarf progenitors. For this purpose, we used the BINSTAR binary evolution code and model MS+WD binary systems, considering different binary interaction mechanisms, such as a tidally enhanced wind mass loss, and a reduced circularisation efficiency. To explore their impact on the second RGB ascent, we compared the modelled orbits with the observed period and eccentricity distributions of Ba and related giants. We show that, independently of the considered mechanism, there is a strong period cut-off below which core-He burning stars should not be found in binary systems with a WD companion. This limit is shorter for more massive RGB stars and for more metal-poor systems. However, we still find a few low-mass short-period giant systems that are difficult to explain with our models, as well as two systems with very high eccentricities.

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