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arXiv 1003.5121astro-ph.SRastro-ph.EP
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行星系统宿主HR\，8799（$λ$ Bootis性质和年龄）物理特性的天文地震测定

Asteroseismic determination of the physical characteristics of the planetary system host HR\,8799 ($λ$ Bootis nature and age)

A. Moya, P. J. Amado, D. Barrado, A. García Hernández, M. Aberasturi, B. Montesinos, F. Aceituno

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4 pages, 2 figures, Proceedings of the HELAS IV International Conference submitted to Astronomische Nachrichten
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摘要：

HR\，8799是一颗$λ$牧夫座，$γ$剑鱼座恒星，拥有一个行星系统和一个有两个环的碎片盘。这使得这个系统成为一个非常有趣的研究目标。特别是，这项工作是致力于确定内部金属的这颗恒星，与它的$λ$牧夫座性质，和它的年龄，利用其$γ$剑鱼座型脉动。为此，我们使用了平衡代码CESAM和非绝热脉动代码GraCo。我们应用频率比方法和时间相关对流理论来估计模式识别、Brunt-Vaïsälä频率积分和模式不稳定性，选择满足所有观测约束的可能模式。使用恒星在HR图中的位置，太阳金属丰度模型被丢弃。这一结果与解释$λ$ Bootis性质的最被接受的假设的主要假设之一相矛盾，该假设是来自具有太阳金属丰度的恒星的气体的吸积/扩散。因此，鉴于这些新的结果，需要对这一假设进行修正。包括精确的内部化学混合是必要的。使用星震学约束条件可以非常精确地确定HR 1，8799的物理特征：年龄范围为[1123，1625]和[26，430]百万年，质量范围分别为[1.32，1.33]和[1.44，1.45] $M_{\odot}$，这取决于视角$i$。这个角度的确定和更精确的X射线光度观测可以确定这颗恒星的质量、金属丰度和年龄。特别是，为了正确理解行星系统，需要准确的年龄估计。在我们的研究中，我们发现广泛用于建模系统的年龄是不同的。

英文摘要：

HR\,8799 is a $λ$ Bootis, $γ$ Doradus star hosting a planetary system and a debris disk with two rings. This makes this system a very interesting target for asteroseismic studies. In particular, this work is devoted to the determination of the internal metallicity of this star, linked with its $λ$ Bootis nature, and its age, taking the advantage of its $γ$ Doradus-type pulsations. To do so we have used the equilibrium code CESAM and the non-adiabatic pulsational code GraCo. We have applied the Frequency Ratio Method and the Time Dependent Convection theory to estimate the mode identification, the Brunt-Vaïsälä frequency integral and the mode instability, making a selection of the possible models fulfilling all observational constraints. Using the position of the star in the HR diagram, the solar metallicity models is discarded. This result contradicts one of the main assumptions of the most accepted hypothesis explaining the $λ$ Bootis nature, the accretion/diffusion of gas from a star with solar metallicity. Therefore, in sight of these new results, a revision of this hypothesis is needed. The inclusion of accurate internal chemical mixing is necessary. The use of the asteroseismological constraints provides a very accurate determination of the physical characteristics of HR\,8799: an age in the ranges [1123, 1625] and [26, 430] Myr, and a mass in the ranges [1.32, 1.33] and [1.44, 1.45] $M_{\odot}$, respectively, depending on the visual angle $i$. The determination of this angle and more accurate multicolor photometric observations can definitively fix the mass, metallicity and age of this star. In particular, an accurate age estimation is needed for a correct understanding of the planetary system. In our study we have found that the age widely used for modelling the system is unlike.

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