arXiv 0905.17222009-05-28astro-ph.SR

恒星振荡的模式寿命--对星震学的意义

Mode lifetimes of stellar oscillations - Implications for asteroseismology

W. J. Chaplin, G. Houdek, C. Karoff, Y. Elsworth, R. New

备注：: letter accepted for publication in A&A
DOI：: 10.1051/0004-6361/200911952

摘要：

成功的星震学推论至少依赖于两件事：恒星中的振荡具有足够大的振幅，可以清楚地观察到;振荡本身足够稳定，可以精确测量模式频率和其他参数。类太阳的p模被对流阻尼，因此模的稳定性取决于寿命。我们寻求一个简单的标度关系之间的平均寿命的最突出的类太阳p模式的恒星，和基本的恒星参数。我们的基础上使用恒星平衡和脉动计算网格的恒星模型的关系，和第一个asteroseisic结果的主序星，次巨星和红巨星的寿命。我们发现，所有三类类太阳恒星的平均寿命的规模一样$T_{\rm eff}^{-4}$（其中$T_{\rm eff}$是有效温度）。当这个关系与著名的Kjeldsen & Bedding（1995）关于窄带强度观测中观测到的模振幅的标度关系相结合时，我们得到了意想不到的结果：频率功率谱中模峰的高度（最大功率谱密度）标度为$g^{-2}$（其中$g$是表面重力）。由于是模态高度（而不是振幅）决定了可以测量模态的信噪比，而且$g$在主序星上变化缓慢，这表明比太阳冷的恒星可能和更热的恒星一样是星震学的好目标。当观察，而不是在多普勒速度，我们的结果意味着模式的高度，然后增加有效温度。

英文摘要：

Successful inference from asteroseismology relies on at least two things: that the oscillations in the stars have amplitudes large enough to be clearly observable; and that the oscillations themselves be stable enough to enable precise measurements of mode frequencies and other parameters. Solar-like p modes are damped by convection, and hence the stability of the modes depends on the lifetime. We seek a simple scaling relation between the mean lifetime of the most prominent solar-like p modes in stars, and the fundamental stellar parameters. We base our search for a relation on use of stellar equilibrium and pulsation computations of a grid of stellar models, and the first asteroseismic results on lifetimes of main-sequence, sub-giant and red-giant stars. We find that the mean lifetimes of all three classes of solar-like stars scale like $T_{\rm eff}^{-4}$ (where $T_{\rm eff}$ is the effective temperature). When this relation is combined with the well-known scaling relation of Kjeldsen & Bedding (1995) for mode amplitudes observed in narrow-band intensity observations, we obtain the unexpected result that the height (the maximum power spectral density) of mode peaks in the frequency power spectrum scales as $g^{-2}$ (where $g$ is the surface gravity). As it is the mode height (and not the amplitude) that fixes the S/N at which the modes can be measured, and as $g$ changes only slowly along the main sequence, this suggests that stars cooler than the Sun might be as good targets for asteroseismology as their hotter counterparts. When observations are instead made in Doppler velocity, our results imply that mode height then does increase with increasing effective temperature.

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