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首页> 外文期刊>PASJ: Publications of the Astronomical Society of Japan >Does the radial–tangential macroturbulence model adequately describe the spectral line broadening of solar-type stars?*
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Does the radial–tangential macroturbulence model adequately describe the spectral line broadening of solar-type stars?*

机译：径向切向大湍流模型是否足以描述太阳型恒星的光谱线展宽？

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摘要

In incorporating the effect of atmospheric turbulence in the broadening of spectral lines, the so-called radial–tangential macroturbulence (RTM) model has been widely used in the field of solar-type stars, which was devised from intuitive appearance of the granular velocity field of the Sun. Since this model assumes that turbulent motions are restricted to only radial and tangential directions, it has a special broadening function with notably narrow width due to the projection effect, the validity of which has not yet been confirmed in practice. With the aim of checking whether this RTM model adequately represents the actual solar photospheric velocity field, we carried out an extensive study on the non-thermal velocity dispersion along the line of sight (Vlos) by analyzing spectral lines at various points of the solar disk based on locally averaged as well as high-spatial-resolution spectra, and found the following results. First, the center-to-limb run of Vlos derived from ground-based low-resolution spectra is simply monotonic with a slightly increasing tendency, which contradicts the specific trend (an appreciable peak at θ ? 45°) predicted from RTM. Second, the Vlos values derived from a large number of spectra based on high-resolution space observation were revealed to follow a nearly normal distribution, without any sign of the peculiar distribution expected for the RTM case. These two observational facts indicate that the actual solar velocity field is not simply dichotomous as assumed in RTM, but directionally more chaotic. We thus conclude that RTM is not an adequate model, at least for solar-type stars, as it would significantly overestimate the turbulent velocity dispersion by a factor of ～2. The classical Gaussian macroturbulence model should be more reasonable in this respect.
机译：在将大气湍流的影响合并到谱线的拓宽中时，所谓的径向切向宏观湍流（RTM）模型已被广泛用于太阳型恒星的领域，该模型是根据颗粒速度场的直观外观而设计的太阳的。由于该模型假定湍流仅限于径向和切线方向，因此它具有特殊的加宽功能，由于投影效果，其宽度特别窄，在实践中尚未证实其有效性。为了检查此RTM模型是否足以代表实际的太阳光球速度场，我们通过分析太阳盘各个点的光谱线，对沿视线（Vlos）的非热速度色散进行了广泛的研究。基于本地平均和高空间分辨率的光谱，得出以下结果。首先，从地面低分辨率谱图得出的Vlos的中心到边缘运行是单调的，具有略微增加的趋势，这与RTM预测的特定趋势（在θ？45°处有明显的峰值）相矛盾。其次，揭示了基于高分辨率空间观察从大量光谱中得出的Vlos值几乎遵循正态分布，而没有任何RTM情况预期的特殊分布的迹象。这两个观察事实表明，实际的太阳速度场不仅如RTM中所假定的那样简单地二分法，而且在方向上更加混乱。因此，我们得出结论，RTM至少对于太阳型恒星不是一个合适的模型，因为它会大大高估湍流速度色散约2倍。在这方面，经典的高斯宏观湍流模型应该更合理。

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