空间分辨日震数据中低信噪比太阳p模式的测量
Measurement of low signal-to-noise-ratio solar p modes in spatially-resolved helioseismic data
摘要：
我们提出了一个适应的旋转校正，m平均光谱技术，旨在观察低信噪比，低频太阳p模式。选择给定（n，l）多重峰的2l+1 m个谱中的每一个的频移，以使m平均谱的似然最大化。高信噪比可以由组合单独的低信噪比、单独的m光谱产生，其中没有一个光谱会产生足够强的峰来测量。我们将该技术应用于龚和MDI的数据，并表明，它使我们能够测量模式与较低的频率比那些与经典的峰值拟合分析的个人-m光谱。我们测量它们的中心频率、分裂、不对称性、寿命和振幅。这种新方法提供的低频、低角和中角对应于对太阳内部深层至核心和辐射内部敏感的模式。此外，低频模式具有更深的上转折点，因此对外层的湍流和磁场以及外部边界条件性质的不确定性不太敏感。由于它们在相同的信噪比下具有更长的寿命（更窄的线宽），因此对较低频率模式的频率的确定更准确，并且所得到的反演应该更精确。
英文摘要：
We present an adaptation of the rotation-corrected, m-averaged spectrum technique designed to observe low signal-to-noise-ratio, low-frequency solar p modes. The frequency shift of each of the 2l+1 m spectra of a given (n,l) multiplet is chosen that maximizes the likelihood of the m-averaged spectrum. A high signal-to-noise ratio can result from combining individual low signal-to-noise-ratio, individual-m spectra, none of which would yield a strong enough peak to measure. We apply the technique to GONG and MDI data and show that it allows us to measure modes with lower frequencies than those obtained with classic peak-fitting analysis of the individual-m spectra. We measure their central frequencies, splittings, asymmetries, lifetimes, and amplitudes. The low-frequency, low- and intermediate-angular degrees rendered accessible by this new method correspond to modes that are sensitive to the deep solar interior down to the core and to the radiative interior. Moreover, the low-frequency modes have deeper upper turning points, and are thus less sensitive to the turbulence and magnetic fields of the outer layers, as well as uncertainties in the nature of the external boundary condition. As a result of their longer lifetimes (narrower linewidths) at the same signal-to-noise ratio the determination of the frequencies of lower-frequency modes is more accurate, and the resulting inversions should be more precise.
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