Spectroscopic and asteroseismic analysis of the remarkable main-sequence A star KIC 11145123
Spectroscopic and asteroseismic analysis of the remarkable main-sequence A star KIC 11145123
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著名主序 A 星 KIC 11145123 的光谱和星震分析
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
T. Sekii
中科院分区：
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作者：
M. Takada;D. Kurtz;H. Shibahashi;S. Murphy;M. Takata;H. Saio;T. Sekii
根据斯巴鲁望远镜的高色散光谱仪观测到的光谱，对KIC 11145123进行了光谱分析，以澄清其性质，这是第一颗具有直接测量的核到面旋转轮廓的主序星。通过分析谱线强度和拟合谱线轮廓，得到了大气参数(Tef=7600K，Log g=4.2，ξ=3.1 Km S−1，[Fe/H]=−0.71Dex)、径向速度、自转速度和元素丰度，并用一维LTE模式计算了这些参数。KIC 11145123的主要特征是：(1)低的[Fe/H]=−0.71±0.11dex和高的径向速度−135.4±0.2 km S−1。这些在晚A恒星中是显著的。我们最好的[Fe/H]较低的星震模型具有稍高的氦丰度和1.4M⊙的低质量。所有这些结果都强烈地表明KIC 11145123是一颗星族II的蓝散星；(2)推算的自转速度证实了恒星缓慢自转的预测；(3)KIC 11145123与AM、AP和蓝散星丰度模式的比较表明，KIC 11145123既不是Am星也不是Ap星，但丰度与蓝散星一致。我们得出的结论是，这颗恒星非常长的100d自转周期是它是蓝色散布星的结果，但形成蓝色散布星的两条途径--双星系统中的合并和质量损失--给我们理解极慢的自转带来了困难。特别是，我们证明没有证据表明存在任何次级伴星，并且我们通过相位调制技术对任何这种据称的伴星的可能质量施加了严格的限制。
A spectroscopic analysis was carried out to clarify the properties of KIC 11145123 – the first main-sequence star with a directly measured core-to-surface rotation profile – based on spectra observed with the High Dispersion Spectrograph (HDS) of the Subaru telescope. The atmospheric parameters (Teff = 7600 K, log g = 4.2, ξ = 3.1 km s−1 and [Fe/H] = −0.71 dex), the radial and rotation velocities, and elemental abundances were obtained by analysing line strengths and fitting line profiles, which were calculated with a 1D LTE model atmosphere. The main properties of KIC 11145123 are: (1) a low [Fe/H] = −0.71 ± 0.11 dex and a high radial velocity of −135.4 ± 0.2 km s−1. These are remarkable among late-A stars. Our best asteroseismic models with this low [Fe/H] have slightly high helium abundance and low masses of 1.4 M⊙. All of these results strongly suggest that KIC 11145123 is a Population II blue straggler; (2) the projected rotation velocity confirms the asteroseismically predicted slow rotation of the star; (3) comparisons of abundance patterns between KIC 11145123 and Am, Ap, and blue stragglers show that KIC 11145123 is neither an Am star nor an Ap star, but has abundances consistent with a blue straggler. We conclude that the remarkably long 100-d rotation period of this star is a consequence of it being a blue straggler, but both pathways for the formation of blue stragglers – merger and mass loss in a binary system – pose difficulties for our understanding of the exceedingly slow rotation. In particular, we show that there is no evidence of any secondary companion star, and we put stringent limits on the possible mass of any such purported companion through the phase modulation technique.