High-precision acoustic helium signatures in 18 low-mass low-luminosity red giants - Analysis from more than four years of Kepler observations
High-precision acoustic helium signatures in 18 low-mass low-luminosity red giants - Analysis from more than four years of Kepler observations
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18 个低质量低光度红巨星的高精度声学氦特征 - 开普勒观测四年多的分析
DOI：
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发表时间：
2015
期刊：
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通讯作者：
Rafael A. García
中科院分区：
文献类型：
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作者：
E. Corsaro;E. Corsaro;J. Ridder;Rafael A. García
上下文由于美国航天局开普勒使命提供的长观测长度和高质量的光变曲线，现在可以获得红巨星中声学模式的高精度频率，从而可以以前所未有的详细程度探测演化的冷低质量恒星的内部。我们利用新的模式频率测量来自四年多的开普勒观测的18个低质量低光度红巨星样本中的氦第二电离区的声学特征。利用贝叶斯程序Diamonds分析了样本恒星径向声学模式的二阶频率差。我们发现，由于氦二次电离的签名，在所有的恒星的样本明确的声学故障。我们可以测量声学深度和声学毛刺的特征宽度，平均精度分别约为~2%和~ 8%。我们发现很好的协议与理论预测和现有的测量文献。最后，我们推导出了二阶差分和频率下Vmax处毛刺信号的幅度，平均精度约为6%，分别获得了0.14−0.24 μHz和0.08−0.33 μHz范围内的值，可用于研究恒星中的氦丰度。
Context. High-precision frequencies of acoustic modes in red giant stars are now available thanks to the long observing length and high quality of the light curves provided by the NASA Kepler mission, thus allowing the interior of evolved cool low-mass stars to be probed with an unprecedented level of detail.Aims. We characterize the acoustic signature of the helium second ionization zone in a sample of 18 low-mass low-luminosity red giants by exploiting new mode-frequency measurements derived from more than four years of Kepler observations.Methods. We analyzed the second frequency differences of radial acoustic modes in all the stars of the sample by using the Bayesian code Diamonds.Results. We find clear acoustic glitches due to the signature of helium second ionization in all the stars of the sample. We could measure the acoustic depth and the characteristic width of the acoustic glitches with a precision level on average around ~2% and ~8%, respectively. We find good agreement with theoretical predictions and existing measurements from the literature. Finally, we derive the amplitude of the glitch signal at νmax for the second differences and for the frequencies with an average precision of ~6%, obtaining values in the range 0.14−0.24 μHz and 0.08−0.33 μHz, respectively, which can be used to investigate the helium abundance in the stars.