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arXiv 1002.3461astro-ph.SR
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低质量类太阳核HD 203608中对流核的生存

Survival of a convective core in low-mass solar-like pulsator HD 203608

S. Deheuvels, E. Michel, M. J. Goupil, J. P. Marques, B. Mosser, M. A. Dupret, Y. Lebreton, B. Pichon, P. Morel

备注：
7 pages, 5 figures Accepted in A&A
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摘要：

2006年8月，使用HARPS对F8 V恒星HD 203608进行了为期5晚的星震观测，随后对数据进行了分析，并对该恒星进行了初步建模（Mosser等人，2008年）。恒星的参数显着的约束，但地震指标（小间距d 01）的行为之一，不能与观察到的，即使是考虑最好的模型。我们研究了通过改变恒星内部的物理性质（d 01对它很敏感）来提高模型与观测之间的一致性的可能性。我们发现，尽管它的质量低，它是可能的生产模型的HD 203608与对流核心。在初步建模中未考虑此类模型。在实践中，我们得到这些模型在这里假设一些额外的混合在早期对流核心的边缘。我们使用Levenberg-Marquardt算法优化模型参数。新的最佳模式与对流核心和观测之间的协议是比没有更好的模式。所有观测参数都在1-sigma观测误差条内拟合。这是第一次观测到像HD 203608这样的低质量老恒星存在对流核心的证据。在低质量恒星的标准模型中，核心在ZAMS之后不久就退出了。核心的生存，直到目前的年龄HD 203608提供了非常强的约束的大小与对流核心相关的混合区。使用过冲作为代理来模拟核心边缘的运输过程，我们发现，要重现全球和地震观测，我们必须有alpha_ov = 0.17 +/- 0.03 Hp HD 203608。我们重新审视的过程中的核心寿命的延长，由于超调的特殊情况下的HD 203608。

英文摘要：

A 5-night asteroseismic observation of the F8V star HD 203608 was conducted in August 2006 with HARPS, followed by an analysis of the data, and a preliminary modeling of the star (Mosser et al. 2008). The stellar parameters were significantly constrained, but the behavior of one of the seismic indexes (the small spacing d01) could not be fitted with the observed one, even with the best considered models. We study the possibility of improving the agreement between models and observations by changing the physical properties of the inner parts of the star (to which d01 is sensitive). We show that, in spite of its low mass, it is possible to produce models of HD 203608 with a convective core. No such model was considered in the preliminary modeling. In practice, we obtain these models here by assuming some extra mixing at the edge of the early convective core. We optimize the model parameters using the Levenberg-Marquardt algorithm. The agreement between the new best model with a convective core and the observations is much better than for the models without. All the observational parameters are fitted within 1-sigma observational error bars. This is the first observational evidence of a convective core in an old and low-mass star such as HD 203608. In standard models of low-mass stars, the core withdraws shortly after the ZAMS. The survival of the core until the present age of HD 203608 provides very strong constraints on the size of the mixed zone associated to the convective core. Using overshooting as a proxy to model the processes of transport at the edge of the core, we find that to reproduce both global and seismic observations, we must have alpha_ov = 0.17 +/- 0.03 Hp for HD 203608. We revisit the process of the extension of the core lifetime due to overshooting in the particular case of HD 203608.

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