论文标题
建模R Coronae Borealis星星：He燃烧壳温度和金属性的影响
Modeling R Coronae Borealis Stars: Effects of He-Burning Shell Temperature and Metallicity
论文作者
论文摘要
R Coronae Borealis（RCB）恒星是极缺乏氢的碳星，产生大量的灰尘，导致亮度突然下降。据信它们主要是通过白矮人合并形成的。在本文中，我们使用MESA来研究与最初燃烧壳温度的合并后对象如何从2.1-5.4 *10^8 k，具有太阳和属极金属率的2.1-5.4 *10^8 k演变为RCB恒星。这些模型最成功的模型具有亚级金属性和接近3 *10^8 k的初始温度。我们发现，对CNO循环中涉及的元素的表面丰度以及RCB的有效温度和半径的差异，对初始He燃烧壳温度有很强的依赖性。涉及核合成的元件呈现约1个dex左右，在10％太阳金属度模型中降低了表面丰度，除了碳和锂外，详细讨论了碳和锂。与太阳能对应物相比，具有生产金属度的模型也具有更长的寿命。此外，我们发现燃烧材料的对流混合仅发生在合并后进化的头几年，此后在RCB阶段和RCB阶段之后的表面丰度是恒定的，提供了为什么这些恒星表现出强烈增强部分He燃烧产品的证据。
The R Coronae Borealis (RCB) stars are extremely hydrogen-deficient carbon stars which produce large amounts of dust, causing sudden deep declines in brightness. They are believed to be formed primarily through white dwarf mergers. In this paper, we use MESA to investigate how post-merger objects with a range of initial He-burning shell temperatures from 2.1 - 5.4 *10^8 K with solar and subsolar metallicities evolve into RCB stars. The most successful model of these has subsolar metallicity and an initial temperature near 3 *10^8 K. We find a strong dependence on initial He-burning shell temperature for surface abundances of elements involved in the CNO cycle, as well as differences in effective temperature and radius of RCBs. Elements involved in nucleosynthesis present around 1 dex diminished surface abundances in the 10% solar metallicity models, with the exception of carbon and lithium which are discussed in detail. Models with subsolar metallicities also exhibit longer lifetimes than their solar counterparts. Additionally, we find that convective mixing of the burned material occurs only in the first few years of post-merger evolution, after which the surface abundances are constant during and after the RCB phase, providing evidence for why these stars show a strong enhancement of partial He-burning products.
