Seismic constraints on the radial dependence of the internal rotation profiles of six Kepler subgiants and young red giants
Seismic constraints on the radial dependence of the internal rotation profiles of six Kepler subgiants and young red giants
复制标题
六颗开普勒亚巨星和年轻红巨星内自转剖面径向依赖性的地震约束
DOI：
10.1051/0004-6361/201322779
复制
发表时间：
2014
影响因子：
6.5
通讯作者：
Goupil
中科院分区：
文献类型：
--
作者：
Deheuvels;Doğan;Goupil
我们仍然不明白是哪种物理机制导致了恒星内部角动量的传输。最近在开普勒亚巨星和红巨星光谱中发现的混合模式包含了旋转的明显特征，这给了我们在这个问题上取得进展的机会。目的我们的目的是探索开普勒目标样本旋转轮廓的径向依赖性。为此，亚巨星和早期红巨星是特别有趣的目标，因为它们的旋转分裂对较深核心外的旋转更敏感，而不是更进化的同类。方法首先提取6颗年轻开普勒巨星的旋转分裂和模态频率。然后，我们使用演化代码Cesam2k和astec对这些恒星进行了地震建模。利用观测到的分裂和最优模型的旋转核，我们反演了六颗恒星的内部旋转曲线。结果我们得到了这些恒星的核心旋转速率的估计值，以及它们的对流包层旋转的上限。我们表明，在亚巨分支期间，核心和包络层之间的旋转对比度增加。我们的结果还表明，亚巨星的核心随着时间的推移而向上旋转，而它们的外壳则向下旋转。对于其中两颗恒星，我们证明了具有深度不连续的不连续旋转剖面比光滑旋转剖面更能再现观测到的分裂。有趣的是，发现的最可能的不连续深度大致与h燃烧壳的位置一致，h燃烧壳将收缩层与膨胀层分开。结论6颗金属丰度不同、主序既有辐射核又有对流核的年轻巨星具有不同的自转模式。这将给恒星角动量输运的场景带来观测限制。此外，如果在年轻红巨星的旋转剖面中存在尖锐的梯度得到证实，预计将有助于区分可能在亚巨星和红巨星分支中传输角动量的物理过程。
ContextWe still do not understand which physical mechanisms are responsible for the transport of angular momentum inside stars. The recent detection of mixed modes that contain the clear signature of rotation in the spectra ofKeplersubgiants and red giants gives us the opportunity to make progress on this question.AimsOur aim is to probe the radial dependence of the rotation profiles for a sample ofKeplertargets. For this purpose, subgiants and early red giants are particularly interesting targets because their rotational splittings are more sensitive to the rotation outside the deeper core than is the case for their more evolved counterparts.MethodsWe first extracted the rotational splittings and frequencies of the modes for six youngKeplerred giants. We then performed a seismic modeling of these stars using the evolutionary codes Cesam2k and astec. By using the observed splittings and the rotational kernels of the optimal models, we inverted the internal rotation profiles of the six stars.ResultsWe obtain estimates of the core rotation rates for these stars, and upper limits to the rotation in their convective envelope. We show that the rotation contrast between the core and the envelope increases during the subgiant branch. Our results also suggest that the core of subgiants spins up with time, while their envelope spins down. For two of the stars, we show that a discontinuous rotation profile with a deep discontinuity reproduces the observed splittings significantly better than a smooth rotation profile. Interestingly, the depths that are found to be most probable for the discontinuities roughly coincide with the location of the H-burning shell, which separates the layers that contract from those that expand.ConclusionsWe characterized the differential rotation pattern of six young giants with a range of metallicities, and with both radiative and convective cores on the main sequence. This will bring observational constraints to the scenarios of angular momentum transport in stars. Moreover, if the existence of sharp gradients in the rotation profiles of young red giants is confirmed, it is expected to help in distinguishing between the physical processes that could transport angular momentum in the subgiant and red giant branches.