The connection between stellar granulation and oscillation as seen by the Kepler mission
The connection between stellar granulation and oscillation as seen by the Kepler mission
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DOI：
10.1051/0004-6361/201424313
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发表时间：
2014-08
影响因子：
6.5
通讯作者：
T. Kallinger;J. Ridder;S. Hekker;S. Mathur;S. Mathur;B. Mosser;M. Gruberbauer;M. Gruberbauer;R. García;C. Karoff;J. Ballot;J. Ballot
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作者：
T. Kallinger;J. Ridder;S. Hekker;S. Mathur;S. Mathur;B. Mosser;M. Gruberbauer;M. Gruberbauer;R. García;C. Karoff;J. Ballot;J. Ballot
上下文开普勒长时间几乎连续的观测显示，在大量恒星样本中存在颗粒背景信号的明确证据，这被解释为对流的表面表现。结果表明，其特征时间尺度和均方根强度起伏与类太阳振荡的峰值频率（νmax）成比例关系。已经进行了各种尝试来量化所观察到的信号，以确定其特征参数的标度关系，并将它们与理论预测进行比较。尽管它们在全球范围内是一致的，但不同方法之间以及观测和模拟之间仍然存在着来源不明的巨大系统差异。目标。我们的目标是研究不同的方法来量化恒星颗粒化的签名，并寻找一个统一的模型，再现所观察到的信号最好的各种各样的恒星。然后，我们的目标是定义的造粒性能和νmax和其他各种恒星参数之间的经验标度关系。方法.我们使用概率的方法来比较不同的方法来提取颗粒信号。我们拟合了大量开普勒目标的功率密度谱，确定了颗粒和全局振荡参数，并量化了它们之间的标度关系。结果我们确定，从太阳和其他一些主序星中已知的功率约为νmax/2的衰减在红巨星中也具有统计学意义，并且具有两个分量的超洛伦兹函数最适合于在脉动功率过剩的更广泛附近再现颗粒信号。我们还建立了背景模型的具体选择可以影响Vmax的确定，引入系统不确定性，可以显着超过随机不确定性。我们发现特征频率（即，相反的时标）和振幅的两个背景分量紧密的尺度与ν最大的各种恒星（约2-2000 μHz的ν最大），并量化后者的质量依赖性。为了与理论预测（不包括观测到的功率下降）进行比较，我们计算了有效时间尺度和辐射热强度波动，发现它们分别近似为τeff g −0.85 T −0.4和Agran（g 2 M）−1/4（或更方便的R/M 3/4）。类似地，热脉动幅度大约为Apul ‡（g 2 M）-1/3（或R 4/3 /M），这隐含地验证了Apul的单独质量和亮度依赖性。我们还检查了我们的缩放关系与太阳参考值，发现它们很好的协议。结论.我们提供了一个彻底的分析，在一个大样本的恒星，我们建立了一个统一的模型，使我们能够准确地提取颗粒和全球振荡参数的颗粒背景信号。由此产生的标度关系允许一个简单的估计的整体光谱形状的任何太阳型振荡器，并可能作为一个起点，为未来的largesample研究或作为一个参考的理论建模的颗粒。
Context. The long and almost continuous observations by Kepler show clear evidence of a granulation background signal in a large sample of stars, which is interpreted as the surface manifestation of convection. It has been shown that its characteristic timescale and rms intensity fluctuation scale with the peak frequency (νmax) of the solar-like oscillations. Various attempts have been made to quantify the observed signal, to determine scaling relations for its characteristic parameters, and to compare them to theoretical predictions. Even though they are consistent on a global scale, large systematic differences of an unknown origin remain between different methods, as well as between the observations and simulations. Aims. We aim to study different approaches to quantifying the signature of stellar granulation and to search for a unified model that reproduces the observed signal best in a wide variety of stars. We then aim to define empirical scaling relations between the granulation properties and νmax and various other stellar parameters. Methods. We use a probabilistic method to compare different approaches to extracting the granulation signal. We fit the power density spectra of a large set of Kepler targets, determine the granulation and global oscillation parameter, and quantify scaling relations between them. Results. We establish that a depression in power at about νmax/2, known from the Sun and a few other main-sequence stars, is also statistically significant in red giants and that a super-Lorentzian function with two components is best suited to reproducing the granulation signal in the broader vicinity of the pulsation power excess. We also establish that the specific choice of the background model can affect the determination of νmax, introducing systematic uncertainties that can significantly exceed the random uncertainties. We find the characteristic frequency (i.e., inverse timescale) and amplitude of both background components to tightly scale with νmax for a wide variety of stars (about 2–2000 μHz in νmax), and quantify a mass dependency of the latter. To enable comparison with theoretical predictions (which do not include the observed power depression), we computed effective timescales and bolometric intensity fluctuations and found them to approximately scale as τeff ∝ g −0.85 T −0.4 and Agran ∝ (g 2 M) −1/4 (or more conveniently R/M 3/4 ), respectively. Similarly, the bolometric pulsation amplitude scales approximately as Apuls ∝ (g 2 M) −1/3 (or R 4/3 /M), which implicitly verifies a separate mass and luminosity dependence of Apuls. We have also checked our scaling relations with solar reference values and find them in good agreement. Conclusions. We provide a thorough analysis of the granulation background signal in a large sample of stars, from which we establish a unified model that allows us to accurately extract the granulation and global oscillation parameter. The resulting scaling relations allow a simple estimate of the overall spectral shape of any solar-type oscillator and might serve as a starting point for future largesample studies or as a reference for theoretical modelling of granulation.