一颗处于MS后收缩阶段的盾牌座三角洲恒星：金牛座44
A delta Scuti star in the post-MS contraction phase: 44 Tauri
摘要：
Scuti delta恒星44 Tau的演化阶段一直不清楚。最近的星震研究已经提出了主序以及主序后演化扩展阶段的模型。然而，这些模型不能同时再现所有观测到的频率，模式不稳定性范围和基本恒星参数。最近的一项测光研究将44 Tau中检测到的独立模式数量增加到15个，新发现的5.30 c/d重力模式扩展了观测到的频率范围。目标。44 Tau的一个可能的进化阶段尚未被考虑：主序列后的整体收缩阶段。我们计算了星震模型，以检验在这个演化阶段的模型是否能更好地拟合观测到的频谱。方法.我们使用Dziembowski的脉动代码来计算径向和非径向模式的非绝热频率。两个径向模式和避免交叉的偶极模式的观察提出了强有力的约束模型。一个双参数过冲例程被用来确定对流核心上方的过冲层中元素混合的效率。结果我们发现，在MS收缩阶段后的脉动模型成功地再现所观察到的频率范围，以及所有个别的径向和非径向模式的频率值。如果假定在小的过冲层中元素有效混合，则7.79 c/d和9.58 c/d混合模的理论频率与观测值更符合。
英文摘要：
The evolutionary stage of the delta Scuti star 44 Tau has been unclear. Recent asteroseismic studies have claimed models on the main sequence, as well as in the expansion phase of the post-main sequence evolution. However, these models could not reproduce all of the observed frequencies, the mode instability range, and the fundamental stellar parameters simultaneously. A recent photometric study has increased the number of detected independent modes in 44 Tau to 15, and a newly found gravity mode at 5.30 c/d extends the observed frequency range. Aims. One of the possible evolutionary stages of 44 Tau has not yet been considered: the overall contraction phase after the main sequence. We computed asteroseismic models to examine whether models in this evolutionary stage provide a better fit of the observed frequency spectrum. Methods. We used Dziembowski's pulsation code to compute nonadiabatic frequencies of radial and nonradial modes. Observation of two radial modes and an avoided crossing of dipole modes put strong constraints on the models. A two-parametric overshooting routine is utilized to determine the efficiency of element mixing in the overshoot layer above the convective core. Results. We find that pulsation models in the post-MS contraction phase successfully reproduce the observed frequency range, as well as the frequency values of all individual radial and nonradial modes. The theoretical frequencies of the mixed modes at 7.79 c/d and 9.58 c/d are in better agreement with the observations if efficient element mixing in a small overshoot layer is assumed.
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