标题： 强耦合或弱耦合：红巨星分支上混合振荡模式的耦合 显示英文标题

标题： Weak or strong: coupling of mixed oscillation modes on the red-giant branch

摘要： 背景。 最近对红巨星的高精度星震观测揭示了其振荡光谱中混合偶极模式的存在。 这些模式允许我们窥探恒星内部。 在用于表征混合模式的参数中，耦合强度q对对流包层底部附近蒸发区附近的恒星结构敏感。 目的。 本工作的目的是探测弱耦合和强耦合近似值的有效性，这两种近似值通常用于沿红巨星分支（RGB）演化过程中计算q。 方法。 为了经验地测试这些近似值，我们在RGB上的恒星模型中分别计算了弱耦合和强耦合极限下的q值，并将其与从振荡方程数值解得到的混合模式频率模式推导出的耦合进行比较。 结果。 我们发现在早期RGB上，当蒸发区位于氢燃烧壳上方的辐射层时，强耦合近似值与之有很好的一致性；而在蒸发区位于对流包层时，则与弱耦合近似值一致。这与早期的研究结果一致。 此外，我们发现，在本研究考虑的质量范围内（1.00 Msun <= M <= 2.00 Msun），在中间状态下使用弱耦合近似值作为q的估计值是可行的。 结论。 蒸发区的宽度可以很好地作为选择哪种近似值的指标。 弱耦合近似值与可观测到的q在两种近似值都不应有效的区域意外地对齐，简化了混合模式属性的渐近计算。 显示英文摘要

摘要： Context. The high precision of recent asteroseismic observations of red-giant stars has revealed the presence of mixed dipole modes in their oscillation spectra. These modes allow for a look inside the stars. Among the parameters used to characterize mixed modes is the coupling strength q, which is sensitive to the stellar structure in the evanescent zone near the bottom of the convective envelope. Aims. The aim of this work is to probe the validity of the weak and strong coupling approximations, commonly used to calculate q, during stellar evolution along the red-giant branch (RGB). Methods. To test the approximations empirically, we calculate q-values in both, the weak and strong limit for stellar models on the RGB and compare them to the coupling derived from the mixed mode frequency pattern obtained from numerical solutions to the oscillation equations. Results. We find good agreement with the strong coupling approximation on the early RGB, when the evanescent zone lies in the radiative layer right above the hydrogen-burning shell; and with the weak coupling approximation once the evanescent zone is situated in the convective envelope. This is consistent with earlier studies. Additionally, we find that it is viable to use the weak coupling approximation as an estimate for q in the intermediate regime, in the mass range considered in this work (1.00 Msun <= M <= 2.00 Msun). Conclusions. The width of the evanescent zone serves as a good measure for which approximation to use. The serendipitous alignment of the weak coupling approximation with the observable q in the regime where neither approximation is expected to be valid simplifies the asymptotic calculation of mixed mode properties.