Constraining Mass-transfer Histories of Blue Straggler Stars with COS Spectroscopy of White Dwarf Companions
Constraining Mass-transfer Histories of Blue Straggler Stars with COS Spectroscopy of White Dwarf Companions
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DOI：
10.3847/1538-4357/ab4273
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发表时间：
2019-04
期刊：
影响因子：
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通讯作者：
N. Gosnell;E. Leiner;R. Mathieu;A. Geller;C. Knigge;A. Sills;N. Leigh
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文献类型：
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作者：
N. Gosnell;E. Leiner;R. Mathieu;A. Geller;C. Knigge;A. Sills;N. Leigh
最近的研究表明，老疏散星团中的大多数蓝离散星（BSS）是由演化的星星向主序星伴星的质量转移形成的，在双星系统中形成BSS和白色矮星（WD）。我们提出的限制在疏散星团NGC188中的两个BSS-WD二进制文件的质量转移的历史，使用WD温度和表面重力测量与哈勃空间望远镜COS远紫外光谱。采用基于Gaia的1847 ± 107 pc的团簇距离，我们确定一个系统，WOCS 4540，通过Case C质量转移形成CO核WD，Teff = K，log g =，对应于质量M_（eff）和冷却年龄M_（yr）。另一个系统WOCS 5379是通过情况B的质量转移形成的，其结果是氦芯WD，Teff = K，log g =，对应于质量为M = 100，年龄为M = 100。WD参数在四个不同的聚类距离假设中是一致的。我们确定可能的祖二进制系统与网格的吸积模型使用MESA，并调查这些系统是否会导致稳定或不稳定的质量传递。WOCS 4540可能是由于在偏心双星系统中近星点通过期间的稳定质量转移，而WOCS 5379挑战了我们目前对红巨星分支恒星质量转移预期结果的理解。这两个系统都是使用详细分析来微调我们对二元进化过程的物理理解的价值的例子。
Recent studies show that the majority of blue straggler stars (BSSs) in old open clusters are formed through mass transfer from an evolved star onto a main-sequence companion, resulting in a BSS and white dwarf (WD) in a binary system. We present constraints on the mass transfer histories of two BSS–WD binaries in the open cluster NGC 188, using WD temperatures and surface gravities measured with Hubble Space Telescope COS far-ultraviolet spectroscopy. Adopting a Gaia-based cluster distance of 1847 ± 107 pc, we determine that one system, WOCS 4540, formed through Case C mass transfer resulting in a CO-core WD with Teff = K and a log g = , corresponding to a mass of M⊙ and a cooling age of Myr. The other system, WOCS 5379, formed through Case B mass transfer resulting in a He-core WD with Teff = K and a log g = , corresponding to a mass of M⊙ and an age of Myr. The WD parameters are consistent across four different cluster distance assumptions. We determine possible progenitor binary systems with a grid of accretion models using MESA, and investigate whether these systems would lead to stable or unstable mass transfer. WOCS 4540 likely resulted from stable mass transfer during periastron passage in an eccentric binary system, while WOCS 5379 challenges our current understanding of the expected outcomes for mass transfer from red giant branch stars. Both systems are examples of the value in using detailed analyses to fine-tune our physical understanding of binary evolutionary processes.