Grid-based seismic modelling at high and low signal-to-noise ratios. HD 181420 and HD 175272
Grid-based seismic modelling at high and low signal-to-noise ratios. HD 181420 and HD 175272
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DOI：
10.1051/0004-6361/201323121
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发表时间：
2014-03
影响因子：
6.5
通讯作者：
S. Hekker;W. Ball
中科院分区：
文献类型：
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作者：
S. Hekker;W. Ball
语境。最近，CoRoT 目标 HD 175272 (F5V) 显示出微弱的类太阳振荡信号，通过差分星震分析（Ozel 等人，2013，A&A，558，A79）相对于地震相似的恒星 HD 181420 (F2V) 进行建模，HD 181420 (F2V) 具有明显的类太阳振荡特征。 Ozel 等人提供的结果。表明 HD 175272 可能具有亚太阳质量，同时比太阳热 1000 K 左右。这似乎不符合物理规律——标准恒星演化理论通常不会预测太阳下质量的太阳金属丰度恒星的温度会高于约 6000 K——因此需要对这颗恒星进行重新分析。目标。我们的目的是比较差分星震分析与基于网格的建模的性能。方法。我们使用两组恒星模型网格和两种网格拟合方法对 HD 175272 和 HD 181420 进行建模，使用它们的有效温度、金属丰度、大频率间隔 (Δν) 和最大振荡功率频率 (νmax) 作为观测约束。结果。我们发现我们能够使用相互兼容且与其他建模工作具有可比性的参数对两颗恒星进行建模。因此，通过适度的光谱和星震输入，我们可以获得恒星参数的合理估计。就 HD 175272 而言，我们基于网格的建模中的恒星参数的不确定性比微分分析中报告的参数更小，因此更具物理性。对于两颗恒星，模型的 νmax 值明显低于报告的观测值。此外，当使用渐近大频率间隔而不是缩放关系来计算 Δν 时，我们发现当忽略 νmax 时，我们的建模结果明显更加自洽。结论。即使在类似太阳振荡较弱的情况下，基于网格的建模也是一种有用的工具。与差分地震学相比，它提供了更精确、更真实的结果。 νmax 的观测值和建模值之间的差异表明，四个观测约束与此处使用的恒星模型并不完全一致，其中 νmax 很可能是这两颗恒星的不一致约束。
Context. Recently, the CoRoT target HD 175272 (F5V), which shows a weak signal of solar-like oscillations, was modelled by a differential asteroseismic analysis (Ozel et al. 2013, A&A, 558, A79) relative to a seismically similar star, HD 181420 (F2V), for which there is a clear signature of solar-like oscillations. The results provided by Ozel et al. indicate the possibility of HD 175272 having subsolar mass, while being of the order of 1000 K hotter than the Sun. This seems unphysical – standard stellar evolution theory generally does not predict solar-metallicity stars of subsolar mass to be hotter than about 6000 K – and calls for a reanalysis of this star. Aims. We aim to compare the performance of differential asteroseismic analysis with that of grid-based modelling. Methods. We use two sets of stellar model grids and two grid-fitting methods to model HD 175272 and HD 181420 using their effective temperatures, metallicities, large frequency separations (Δν), and frequencies of maximum oscillation power (νmax) as observational constraints. Results. We find that we are able to model both stars with parameters that are both mutually compatible and comparable with other modelling efforts. Hence, with modest spectroscopic and asteroseismic inputs, we obtain reasonable estimates of stellar parameters. In the case of HD 175272, the uncertainties of the stellar parameters from our grid-based modelling are smaller, and hence more physical, than those reported in the differential analysis. For both stars, the models have significantly lower values of νmax than the reported observed values. Furthermore, when using the asymptotic large frequency separation as opposed to the scaling relation to compute Δν, we find that our modelling results are significantly more self-consistent when νmax is ignored. Conclusions. Grid-based modelling is a useful tool even in cases of weak solar-like oscillations. It provides more precise and more realistic results than obtained with differential seismology. The difference in the observed and modelled values of νmax indicates that the four observational constraints are not fully consistent with the stellar models used here, with νmax most likely to be the inconsistent constraint for these two stars.