ASTEROSEISMIC ANALYSIS OF THE INTERNAL STRUCTURE AND EVOLUTION OF RED GIANT BRANCH BUMP STARS
ASTEROSEISMIC ANALYSIS OF THE INTERNAL STRUCTURE AND EVOLUTION OF RED GIANT BRANCH BUMP STARS
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DOI：
10.1088/0004-637x/804/1/6
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发表时间：
2015-05
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影响因子：
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通讯作者：
N. Gai;Yanke Tang
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作者：
N. Gai;Yanke Tang
“凸点”是星团红巨星分支（RGB）光度函数的一个显著特征。通过构造不同质量和金属丰度的模型网格来研究RGB凸点的亮度特征，发现对于给定的金属丰度，亮度几乎随质量的增加而单调增加，随金属丰度的增加而单调减少。此外，不同的恒星有不同形状的RGB凸起。它与H不连续的尖锐性相关，H不连续是在第一次疏浚期间由对流包络留下的。利用小间距d 01，d10的周期性来探测内部结构，我们发现，在大约一半的声学半径处，声速有一个急剧的变化，这是由第一绝热指数Γ 1？>在第二氦电离区。它在d 01、d10产生一个周期为6.4 μ Hz的振荡调制。同时，在同一模式中，对流包络的底部位于一个相对较小的声学半径tenvp/ T？>，约为10 - 1。它太深了，无法探测到对流层底部的确切位置。为了区分不同恒星的演化状态，我们计算了渐近g模周期间隔Δ 1？> .我们发现Δ 1？>随着进化而单调下降。它是一个可靠的参数，用于区分在RGB凹凸的不同位置的恒星。
The “bump” is a prominent feature of the red giant branch (RGB) luminosity function of stellar clusters. Through constructing a grid of models with different masses and metallicities to study the feature of the RGB bump luminosity we find that the luminosity increases almost monotonically with increasing mass for a given metallicity and decreases monotonically with increasing metallicity. Moreover, different stars have different shapes of the RGB bump. It is correlated with the sharpness of the H discontinuity, which is left over by the convection envelope during the first dredge-up. Using the periodicity in the small separations d01, d10 to probe the internal structure, we find that, at about half the acoustic radius, the sound speed has a sharp variation that is caused by a local depression of the first adiabatic exponent Γ 1 ?> in the second helium ionization zone. It induces an oscillation modulation in d01, d10 with a period of 6.4 μ Hz. Meanwhile, in the same model, the base of the convective envelope is located at a relatively small acoustic radius t envp / T ?> , which is about 10−1. It is too deep to detect the exact location of the bottom of the outer convective envelope. In order to discriminate the evolutionary status of different stars, we calculate the asymptotic g-mode period spacing Δ &Pgr; 1 ?> . We find that Δ &Pgr; 1 ?> decreases monotonically with evolution. It is a reliable parameter for distinguishing stars in different positions of the RGB bump.