Blocking Metal Accretion onto Population III Stars by Stellar Wind
Blocking Metal Accretion onto Population III Stars by Stellar Wind
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DOI：
10.3847/1538-4357/aa7e2c
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发表时间：
2017-07
期刊：
影响因子：
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通讯作者：
S. Tanaka;G. Chiaki;N. Tominaga;H. Susa
中科院分区：
文献类型：
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作者：
S. Tanaka;G. Chiaki;N. Tominaga;H. Susa
低质量第三星族（PopIII）恒星可以存活到现在。在我们的银河系中没有检测到低质量的PopIII恒星，这已经对PopIII恒星的初始质量函数（IMF）提出了严格的限制，这表明PopIII恒星具有头重脚轻的IMF。另一方面，有些人声称缺乏这样的恒星是由于星际介质（ISM）中重元素的吸积导致其表面的金属富集。我们调查的恒星风对金属吸积到低质量的PopIII恒星的影响，因为吸积的本地ISM到太阳上的太阳风，即使是中性的。低质量PopIII恒星的恒星风和辐射是基于附近的低质量恒星系统（包括我们的太阳）的知识建模的。我们发现，低质量的PopIII恒星穿越银河系形成恒星磁层在他们的大部分生活。一旦磁层形成，大多数中性星际粒子在到达恒星表面之前就会被光电离，并被风吹走。特别是铁的吸积丰度与Bondi-Hoyle-Lyttleton吸积相比将降低1倍。金属吸积只能将铁的丰度[Fe/H]提高到14。这表明，低质量的PopIII恒星仍然是原始的，将被发现作为无金属的恒星，并进一步寻找他们是有价值的限制IMF的PopIII恒星。
Low-mass population III (PopIII) stars of could survive up until the present. The nondetection of low-mass PopIII stars in our Galaxy has already put a stringent constraint on the initial mass function (IMF) of PopIII stars, suggesting that PopIII stars have a top-heavy IMF. On the other hand, some claim that the lack of such stars stems from metal enrichment of their surfaces by the accretion of heavy elements from the interstellar medium (ISM). We investigate the effects of the stellar wind on metal accretion onto low-mass PopIII stars because accretion of the local ISM onto the Sun is prevented by the solar wind, even for neutrals. The stellar wind and radiation of low-mass PopIII stars are modeled based on knowledge of nearby low-mass stellar systems, including our Sun. We find that low-mass PopIII stars traveling across the Galaxy form a stellar magnetosphere in most of their life. Once the magnetosphere is formed, most of the neutral interstellar particles are photoionized before reaching the stellar surface and are blown away by the wind. Especially, the accretion abundance of iron will be reduced by a factor of compared with Bondi–Hoyle–Lyttleton accretion. The metal accretion can enhance iron abundance [Fe/H] only up to ∼−14. This demonstrates that low-mass PopIII stars remain pristine and will be found as metal-free stars and that further searches for them are valuable in constraining the IMF of PopIII stars.