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arXiv 1702.04773astro-ph.SR
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VLT-FLAMES狼蛛调查XXVI:30只剑鱼中O型侏儒种群的特性

The VLT-FLAMES Tarantula Survey XXVI: Properties of the O-dwarf population in 30 Doradus

C. Sabín-Sanjulián, S. Simón-Díaz, A. Herrero, J. Puls, F. R. N. Schneider, C. J. Evans, M. Garcia, F. Najarro, I. Brott, N. Castro, P. A. Crowther, A. de Koter… 展开作者

C. Sabín-Sanjulián, S. Simón-Díaz, A. Herrero, J. Puls, F. R. N. Schneider, C. J. Evans, M. Garcia, F. Najarro, I. Brott, N. Castro, P. A. Crowther, A. de Koter, S. E. de Mink, G. Gräfener, N. J. Grin, G. Holgado, N. Langer, D. J. Lennon, J. Maíz Apellániz, O. H. Ramírez-Agudelo, H. Sana, W. D. Taylor, J. S. Vink, N. R. Walborn

摘要:

VLT-火焰狼蛛巡天在大麦云(LMC)的剑鱼座30区域观测到数百颗O型恒星。我们研究了105个明显的单O型矮星的性质。为了确定恒星和风参数,我们使用了IACOB-GBAT软件包,这是一个基于用FASTWIND代码计算的大网格大气模型的自动程序。除了经典的技术,我们应用贝叶斯BONSAI工具来估计进化质量。我们提供了一个新的校准的有效温度与光谱类型的O型矮星在大麦哲伦星系,基于我们的均匀分析的最大样本的这样的对象,包括所有的光谱亚型。与以前的结果很好的协议被发现,虽然采样在最早的亚型可以改进。在演化背景下研究了自转速率和氦丰度。我们发现,在我们的样本中,大多数快速旋转(vsini高于300公里/秒)的质量低于25 MSun和中间旋转校正的重力(log gc在3.9和4.1之间)。这样的快速旋转者在较高的重力下(即较年轻的年龄)是罕见的,在较低的重力下(较大的年龄)是不存在的。这是不期望从理论进化模型,并没有出现是由于在我们的样本中的选择偏差。我们比较了估计的进化和光谱质量,发现一个趋势,即前者是更高的质量低于20 MSun。这可以解释为将我们的样本限制在O型恒星上的结果,我们没有看到系统质量差异的令人信服的证据。对于样本中的大多数恒星,我们无法可靠地估计风强度参数(因此质量损失率),特别是对于光度低于logL/LSun约5.1的天体。紫外光谱学需要对这些矮星的风特性进行详细的研究。

英文摘要:

The VLT-FLAMES Tarantula Survey has observed hundreds of O-type stars in the 30 Doradus region of the Large Magellanic Cloud (LMC). We study the properties of 105 apparently single O-type dwarfs. To determine stellar and wind parameters, we used the IACOB-GBAT package, an automatic procedure based on a large grid of atmospheric models calculated with the FASTWIND code. In addition to classical techniques, we applied the Bayesian BONNSAI tool to estimate evolutionary masses. We provide a new calibration of effective temperature vs. spectral type for O-type dwarfs in the LMC, based on our homogeneous analysis of the largest sample of such objects to date and including all spectral subtypes. Good agreement with previous results is found, although the sampling at the earliest subtypes could be improved. Rotation rates and helium abundances are studied in an evolutionary context. We find that most of the rapid rotators (vsini higher than 300 km/s ) in our sample have masses below 25 MSun and intermediate rotation-corrected gravities (log gc between 3.9 and 4.1). Such rapid rotators are scarce at higher gravities (i.e. younger ages) and absent at lower gravities (larger ages). This is not expected from theoretical evolutionary models, and does not appear to be due to a selection bias in our sample. We compare the estimated evolutionary and spectroscopic masses, finding a trend that the former is higher for masses below 20 MSun. This can be explained as a consequence of limiting our sample to the O-type stars, and we see no compelling evidence for a systematic mass discrepancy. For most of the stars in the sample we were unable to estimate the wind-strength parameter (hence mass-loss rates) reliably, particularly for objects with luminosity lower than logL/LSun about 5.1. Ultraviolet spectroscopy is needed to undertake a detailed investigation of the wind properties of these dwarfs.

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