The Red-giant Branch Bump Revisited: Constraints on Envelope Overshooting in a Wide Range of Masses and Metallicities
The Red-giant Branch Bump Revisited: Constraints on Envelope Overshooting in a Wide Range of Masses and Metallicities
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重新审视红巨星分支凸点：在各种质量和金属丰度下对包络超调的限制
DOI：
10.3847/1538-4357/aabf90
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
J. Montalb'an
中科院分区：
文献类型：
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作者：
Saniya Khan;O. Hall;A. Miglio;G. Davies;B. Mosser;L. Girardi;J. Montalb'an
红巨星的分支碰撞为研究低质量恒星的内部结构提供了有价值的信息。由于目前的模型不能准确地预测对流边界以外混合过程的发生和效率，人们可以使用凸起的光度--在第一次向上疏浚期间对流包络的最大扩展的诊断--作为此类过程的校准器。通过结合小行星地震和光谱约束，我们将对凸起的分析扩展到质量和金属含量，而不是以前使用球状星团可以获得的质量和金属含量。我们的数据集包括开普勒观测的近3000颗红巨星和远地点光谱。利用统计混合模型，我们能够在平均地震参数νmax和中检测到凸起，并表明它的观测位置揭示了质量和金属丰度的总体趋势，与模型的预期一致。此外，我们的分析表明，标准恒星模型低估了有效混合包络的深度。由于包含了来自对流包层底部的显著超调，其效率随着金属丰度的降低而增加，这使得我们能够重现观察到的凸起位置。有趣的是，这一趋势在以前的球状星团研究中也有报道。
The red-giant branch bump provides valuable information for the investigation of the internal structure of low-mass stars. Because current models are unable to accurately predict the occurrence and efficiency of mixing processes beyond convective boundaries, one can use the luminosity of the bump—a diagnostic of the maximum extension of the convective envelope during the first-dredge up—as a calibrator for such processes. By combining asteroseismic and spectroscopic constraints, we expand the analysis of the bump to masses and metallicities beyond those previously accessible using globular clusters. Our data set comprises nearly 3000 red-giant stars observed by Kepler and with APOGEE spectra. Using statistical mixture models, we are able to detect the bump in the average seismic parameters νmax and , and show that its observed position reveals general trends with mass and metallicity in line with expectations from models. Moreover, our analysis indicates that standard stellar models underestimate the depth of efficiently mixed envelopes. The inclusion of significant overshooting from the base of the convective envelope, with an efficiency that increases with decreasing metallicity, allows us to reproduce the observed location of the bump. Interestingly, this trend was also reported in previous studies of globular clusters.