论文标题
为什么二进制相互作用不一定统治低金属性的狼射线星的形成
Why binary interaction does not necessarily dominate the formation of Wolf-Rayet stars at low metallicity
论文作者
论文摘要
经典的狼射线（WR）恒星是巨大的，氢耗尽的，后序列的恒星，表现出发射线主导的光谱。对于给定的金属z，超过一定初始质量m_single（z）的恒星可以通过固有的质量损失（单星通道）到达WR相。较低肿块的恒星可以通过二进制传质（二进制通道）到达WR相。通常认为，二进制通道在较低Z（例如SMC和LMC）的环境中占主导地位WR恒星的形成。但是，他们报告的WR二元分数为30-40％，与银河系相当。在这里，我们通过考虑将剥离产品以WR恒星出现所需的最小初始质量M_SPEC（Z）来解释这一明显的矛盾。我们使用云和银河系中的最低亮度WR星校准M_SPEC（Z）。使用各种演进代码探索了一系列M_Single（Z）值。我们通过考虑间隔[m_spec（z），m_single（z）]来估计二进制通道的其他贡献，该间隔表征了二进制文件可以形成其他WR恒星的初始质量范围。 结果：在Galaxy，LMC和SMC中，WR-PhenoMenon停止了Logl = 4.9、5.25和5.6 [LSUN]的发光度以下，它将HE-Star群体转化为7.5、11、17 MSUN的质量和M_SPEC = 18、23、23、37 MSUN的初始质量。在各个星系中具有较低初始质量的剥离恒星往往不会以WR恒星的形式出现。 M_Single位于Galaxy，LMC和SMC的20-30、30-60和> 40 msun范围内。我们发现，二进制通道的额外贡献是Z的非平凡函数，不能最终声称随着Z的降低而单调地增加了单调的增加。因此，一个人不应希望A-Priori期望二进制相互作用在低Z形成WR恒星中变得越来越重要，或者随着WR二进制的增长而随着Z的减少而变得越来越重要。
Classical Wolf-Rayet (WR) stars are massive, hydrogen depleted, post main-sequence stars that exhibit emission-line dominated spectra. For a given metallicity Z, stars exceeding a certain initial mass M_single(Z) can reach the WR phase through intrinsic mass-loss (single-star channel). Stars of lower masses can reach the WR phase via binary mass transfer (binary channel). It is commonly assumed that the binary channel dominates the formation of WR stars in environments with low Z such as the SMC and LMC. However, their reported WR binary fractions of 30-40% are comparable to that of the Galaxy. Here, we explain this apparent contradiction by considering the minimum initial mass M_spec(Z) needed for the stripped product to appear as a WR star. We calibrate M_spec(Z) using the lowest-luminosity WR stars in the Clouds and the Galaxy. A range of M_single(Z) values are explored using various evolution codes. We estimate the additional contribution of the binary channel by considering the interval [M_spec(Z), M_single(Z)], which characterises the initial-mass range in which binaries can form additional WR stars. Results: The WR-phenomenon ceases below luminosities of logL = 4.9, 5.25, and 5.6 [Lsun] in the Galaxy, LMC, and SMC, which translates to He-star masses of 7.5, 11, 17 Msun and initial masses of M_spec = 18, 23, 37 Msun. Stripped stars with lower initial masses in the respective galaxies would tend to not appear as WR stars. M_single lies in the range 20-30, 30-60, and > 40 Msun for the Galaxy, LMC, and SMC. We find that that the additional contribution of the binary channel is a non-trivial function of Z that cannot be conclusively claimed to be monotonically increasing with decreasing Z. Hence, one should not a-priori expect that binary interactions become increasingly important in forming WR stars at low Z, or that the WR binary fraction grows with decreasing Z.
