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arXiv 2303.11209astro-ph.SR
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沃尔夫-拉叶星WN3/O3型的双星性质约束

Constraints on the Binarity of the WN3/O3 Class of Wolf-Rayet Stars

Philip Massey, Kathryn F. Neugent, Nidia I. Morrell

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AI总结：

本研究针对麦哲伦云中发现的WN3/O3型沃尔夫-拉叶星，通过多年视向速度观测排除了其拥有大质量伴星的可能，推测它们是大质量恒星演化中正常的短寿命阶段。

摘要：

WN3/O3型沃尔夫-拉叶星（Wolf-Rayet star，简称WR星）是我们在麦哲伦云WR星巡天过程中发现的天体。这类恒星同时呈现高激发态WN星的发射线与高温O型星的吸收线，但我们此前的研究已证实，吸收光谱是该WR星自身的固有特征。它们在大质量恒星演化过程中所处的位置至今尚不明确。本文我们探究了这类恒星是双星演化产物的可能性。尽管它们并非WN3+O3~V双星系统，但仍有可能存在未被观测到的伴星。为验证这一可能性，我们对已知9颗WN3/O3型星中的6颗开展了持续多年的视向速度研究。研究未发现具有统计显著性的视向速度变化证据，据此我们对假设存在的伴星质量设定了严格的上限：在大概率的轨道倾角下，轨道周期小于100天的伴星质量必须小于2倍太阳质量（2M☉）；轨道周期小于10天的伴星，质量则必须小于1倍太阳质量（1M☉）。我们认为，这类伴星为致密天体的可能性极低。吸收线显示其投影自转速度处于正常水平，说明这类恒星不太可能是通过伴星并合完成演化的。偏低的自转速度也表明，它们并非均匀演化的产物。因此，这类恒星很可能是大质量恒星演化过程中一个正常但寿命较短的阶段。

英文摘要：

The WN3/O3 Wolf-Rayet (WR) stars were discovered as part of our survey for WRs in the Magellanic Clouds. The WN3/O3s show the emission lines of a high-excitation WN star and the absorption lines of a hot O-type star, but our prior work has shown that the absorption spectrum is intrinsic to the WR star. Their place in the evolution of massive stars remains unclear. Here we investigate the possibility that they are the products of binary evolution. Although these are not WN3+O3~V binaries, they could still harbor unseen companions. To address this possibility, we have conducted a multi-year radial velocity study of six of the nine known WN3/O3s. Our study finds no evidence of statistically significant radial velocity variations, and allows us to set stringent upper limits on the mass of any hypothetical companion star: for probable orbital inclinations, any companion with a period less than 100 days must have a mass less than 2Mo. For periods less than 10 days, any companion would have to have a mass less than 1Mo. We argue that scenarios where any such companion is a compact object are unlikely. The absorption lines indicate a normal projected rotational velocity, making it unlikely that these stars evolved with the aid of a companion star that has since merged. The modest rotation also suggests that these stars are not the result of homogenous evolution. Thus it is likely that these stars are a normal but short-lived stage in the evolution of massive stars.

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