The Wolf-Rayet stars in M 31. I. Analysis of the late-type WN stars
The Wolf-Rayet stars in M 31. I. Analysis of the late-type WN stars
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M 31中的沃尔夫-拉叶星I晚型WN星分析
DOI：
10.1051/0004-6361/201323240
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发表时间：
2014
影响因子：
6.5
通讯作者：
W.-R. Hamann
中科院分区：
文献类型：
--
作者：
A. Sander;H. Todt;R. Hainich;W.-R. Hamann
背景沃尔夫-拉叶星的综合研究在过去进行了银河系和LMC人口。结果显示了这些不同星系的WR种群之间的显着差异，但也有意想不到的相似之处。对M31中WR星的分析将有助于加深我们对这些天体在不同星系环境中的认识。恒星和风参数将告诉在其他星系的WR星的形成与不同的金属丰度和星星形成历史。所获得的参数将为大质量恒星在M31环境中的演化提供约束。方法采用最新版本的波茨坦Wolf-Rayet大气模型程序，通过拟合光谱和光度数据，对恒星进行分析。要占后期WN 10和WN 11亚型的相对较低的温度，我们的WN模型已扩展到这个温度regiment.ResultsStellar和大气参数推导出所有已知的晚型WN星在M 31可用的光谱。所有这些恒星的外层仍然有氢，其中一些质量高达50%。在赫罗图中，这些恒星位于零年主序星的冷端，光度在105 - 106 L <$。值得注意的是，没有一颗星星的质量超过106 L。结论M31中的晚型WN星如果是通过单颗星星演化形成的，则起源于20 ~ 60 M的初始质量。在极晚型WN 9 -11星中，只有一颗星星位于剑鱼座S不稳定带。我们没有发现任何晚型WN星在银河系中已知的高光度。
ContextComprehensive studies of Wolf-Rayet stars were performed in the past for the Galactic and the LMC population. The results revealed significant differences, but also unexpected similarities between the WR populations of these different galaxies. Analyzing the WR stars in M 31 will extend our understanding of these objects in different galactic environments.AimsThe present study aims at the late-type WN stars in M 31. The stellar and wind parameters will tell about the formation of WR stars in other galaxies with different metallicity and star formation histories. The obtained parameters will provide constraints to the evolution of massive stars in the environment of M 31.MethodsWe used the latest version of the Potsdam Wolf-Rayet model atmosphere code to analyze the stars via fitting optical spectra and photometric data. To account for the relatively low temperatures of the late WN10 and WN11 subtypes, our WN models have been extended into this temperature regime.ResultsStellar and atmospheric parameters are derived for all known late-type WN stars in M 31 with available spectra. All of these stars still have hydrogen in their outer envelopes, some of them up to 50% by mass. The stars are located on the cool side of the zero age main sequence in the Hertzsprung-Russell diagram, while their luminosities range from 105to 106L⊙. It is remarkable that no star exceeds 106L⊙.ConclusionsIf formed via single-star evolution, the late-type WN stars in M 31 stem from an initial mass range between 20 and 60M⊙. From the very late-type WN9-11 stars, only one star is located in the S Doradus instability strip. We do not find any late-type WN stars with the high luminosities known in the Milky Way.