A quantitative study of O stars in NGC 2244 and the Monoceros OB2 association
A quantitative study of O stars in NGC 2244 and the Monoceros OB2 association
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DOI：
10.1051/0004-6361/201117458
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发表时间：
2011-10
影响因子：
6.5
通讯作者：
F. Martins;L. Mahy;G. Rauw;D. University;L. University;P. University
中科院分区：
文献类型：
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作者：
F. Martins;L. Mahy;G. Rauw;D. University;L. University;P. University
目标。我们的目标是确定NGC 2244星团中的7颗O型恒星和风的特性，以及OB星团monob2中的3颗O型恒星。这些性质让我们了解到O型恒星的质量损失率。它们使我们能够检查大质量恒星中旋转混合的有效性，并更好地了解电离通量和风机械能释放对周围星际介质的影响及其对触发恒星形成的影响。方法。我们收集了目标恒星的光学和紫外光谱，并通过CMFGEN代码计算的大气模型进行了分析。对双星的光谱进行了解缠，并分别对其组成进行了研究。结果。所有恒星的演化年龄都小于500万年，其中质量最大的恒星是最年轻的恒星。氮表面丰度与预计的旋转速度没有明显的关系。双星和单星显示出相同的富集范围。这是由于二元系统的年轻和/或广泛分离，其中的组成部分（尚未）经历强烈的相互作用。我们观察到，在光度较高的天体中，有明显的富集趋势，这与旋转演化模型对任何给定年龄的O型恒星群的预测相一致。我们证实了后期O型矮星的风的微弱。一般来说，由紫外线得到的质量损失率低于由Hα得到的质量损失率。最新型矮星的紫外质量损失率甚至低于单线驱动极限。这些问题是在大质量恒星风结构的背景下讨论的。演化质量和光谱质量在25 M以上是一致的，但不确定性很大。在这个阈值以下，这里研究的少数晚O型恒星表明，质量差异似乎仍然存在。
Aims. Our goal is to determine the stellar and wind properties of seven O stars in the cluster NGC 2244 and three O stars in the OB association Mon OB2. These properties give us insight into the mass loss rates of O stars. They allow us to both check the validity of rotational mixing in massive stars and to better understand the effects of the ionizing flux and wind mechanical energy release on the surrounding interstellar medium and its influence on triggered star formation. Methods. We collected optical and UV spectra of the target stars that we analyzed by means of atmosphere models computed with the code CMFGEN. The spectra of binary stars were disentangled and the components studied separately. Results. All stars have an evolutionary age less than 5 million years, with the most massive stars being among the youngest. Nitrogen surface abundances show no clear relation with projected rotational velocities. Binaries and single stars show the same range of enrichment. This is attributed to the youth and/or wide separation of the binary systems in which the components have not (yet) experienced strong interaction. A clear trend toward greater enrichment in higher luminosity objects is observed, consistent with what evolutionary models with rotation predict for a population of O stars at any given age. We confirm the weakness of winds in late O dwarfs. In general, mass loss rates derived from UV lines are lower than mass loss rates obtained from Hα. The UV mass loss rates are even lower than the single-line driving limit in the latest type dwarfs. These issues are discussed in the context of the structure of massive stars winds. The evolutionary and spectroscopic masses are in agreement above 25 M� , but the uncertainties are large. Below this threshold, the few late-type O stars studied here indicate that the mass discrepancy still seems to hold.