Surface-effect corrections for oscillation frequencies of evolved stars
Surface-effect corrections for oscillation frequencies of evolved stars
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DOI：
10.1051/0004-6361/201630260
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发表时间：
2017-02
影响因子：
6.5
通讯作者：
W. Ball;W. Ball;W. Ball;L. Gizon;L. Gizon;L. Gizon
中科院分区：
文献类型：
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作者：
W. Ball;W. Ball;W. Ball;L. Gizon;L. Gizon;L. Gizon
上下文。对类太阳振子的精确建模要求对建模的模态频率进行校正，以消除由于对近地表层建模不当而引起的系统偏移，即所谓的表面效应。表面效应的几个参数化现在是可用的，但它们还没有被系统地与显示混合g -和p -模式特征的恒星的观测进行比较。目标。我们研究了我们对表面效应的功能形式的不确定性给恒星模型参数引入了多少额外的不确定性。同时，我们测试了在模拟观测到的亚巨星和低光度红巨星时，任何参数化是否明显更好或更差。方法。我们对开普勒观测到的六颗恒星进行了建模，这些恒星显示出清晰的混合模式。我们固定了恒星模型的输入物理，并在五个参数化之间改变表面校正的选择。结果。使用太阳校准的幂律校正的模型始终比其他四种校正更不适合观测结果。其余四种修正的模型一般都能很好地拟合观测结果，Ball和Gizon的联合地表修正可能略好一些。在约2 σ的不确定度范围内，模型参数的拟合大致一致，修正洛伦兹法和自由幂律修正之间的差异有时超过3 σ水平。相对于最佳拟合值，恒星的质量、半径和年龄的总不确定性分别小于2%、1%和6%。结论。由Kjeldsen等人制定的太阳校准幂律似乎不适合用于更进化的类太阳振荡器。在其余的表面修正中，由表面效应引入的模型参数的不确定性大约是这六颗恒星的单个拟合的不确定性的两倍。尽管由于我们对如何管理表面效应的不确定性，这些拟合结果在某种程度上不太确定，但这些结果也表明，模拟亚巨星和低光度红巨星的单个模式频率是可行的，因此也可以使用这些单个恒星来帮助约束恒星模型。
Context. Accurate modelling of solar-like oscillators requires that modelled mode frequencies are corrected for the systematic shift caused by improper modelling of the near-surface layers, known as the surface effect. Several parametrizations of the surface effect are now available but they have not yet been systematically compared with observations of stars showing modes with mixed g - and p -mode character. Aims. We investigate how much additional uncertainty is introduced to stellar model parameters by our uncertainty about the functional form of the surface effect. At the same time, we test whether any of the parametrizations is significantly better or worse at modelling observed subgiants and low-luminosity red giants. Methods. We model six stars observed by Kepler that show clear mixed modes. We fix the input physics of the stellar models and vary the choice of surface correction between five parametrizations. Results. Models using a solar-calibrated power law correction consistently fit the observations more poorly than the other four corrections. Models with the remaining four corrections generally fit the observations about equally well, with the combined surface correction by Ball & Gizon perhaps being marginally superior. The fits broadly agree on the model parameters within about the 2 σ uncertainties, with discrepancies between the modified Lorentzian and free power law corrections occasionally exceeding the 3 σ level. Relative to the best-fitting values, the total uncertainties on the masses, radii and ages of the stars are all less than 2, 1 and 6 per cent, respectively. Conclusions. A solar-calibrated power law, as formulated by Kjeldsen et al., appears unsuitable for use with more evolved solar-like oscillators. Among the remaining surface corrections, the uncertainty in the model parameters introduced by the surface effects is about twice as large as the uncertainty in the individual fits for these six stars. Though the fits are thus somewhat less certain because of our uncertainty of how to manage the surface effect, these results also demonstrate that it is feasible to model the individual mode frequencies of subgiants and low-luminosity red giants, and hence also use these individual stars to help to constrain stellar models.