论文标题

沿着红色巨型分支的二进制进化与Binstar:钡星观点

Binary evolution along the Red Giant Branch with BINSTAR: The barium star perspective

论文作者

Escorza, Ana, Siess, Lionel, Van Winckel, Hans, Jorissen, Alain

论文摘要

钡(BA),CH和外部或TC-Poor S型星是进化的低和中间质量星,表面显示出慢速中性体接合过程的增强,这表明从以前的渐近巨型分支(AGB)同伴(现在是白色Dwarf(Wd wd wd wd dd dd dd dd dd wd dd dd dd dd dd dd ddwarf),它表现出了质量积聚。 BA和CH星可以在主要序列(MS),次巨头和巨型相中找到,而外部S型恒星仅填充巨型分支。随着这些污染的恒星的发展,它们可能参与了与现在白矮人伴侣的第二阶段相互作用。在本文中,我们考虑了由前序列BA星和WD伴侣组成的系统,当前者沿着红色巨型分支(RGB)演变时。我们要确定是否可以根据其可疑矮人的祖细胞的进化来推断已知的Ba,CH和S巨人的轨道特性。为此,我们考虑了不同的二进制相互作用机制,例如潮汐增强的风量损失和降低的圆形化效率。为了探索它们对第二个RGB上升的影响,我们将建模的轨道与观察到的时期和相关巨头的偏心分布进行了比较。我们表明,与所考虑的机制无关,有一个很强的时期,在以下是核心燃烧的恒星中,在具有WD伴侣的二元系统中找不到。对于更大的RGB恒星和更多的金属贫困系统而言,此极限较短。但是,我们仍然发现一些低质量的短周期巨型系统,这些系统很难用我们的模型解释以及两个具有很高偏心率的系统。

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 (AGB) 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 use 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 compare 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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