Abstract

Microturbulence, macroturbulence, thermal motion, and rotation contribute to the broadening of line profiles in stellar spectra. Reliable data on the velocity distribution of turbulent motions in stellar atmospheres are needed to interpret the spectra of solar-type stars unambiguously in exoplanetary research. Stellar spectra with a high resolution of 115 000 obtained with the HARPS spectrograph provide an opportunity to examine turbulence velocities and their depth distributions in the photosphere of stars. Fourier analysis was performed for 17 iron lines in the spectra of 13 stars with an effective temperature of 4900–6200 K and a logarithm of surface gravity of 3.9–5.0 as well as in the spectrum of the Sun as a star. Models of stellar atmospheres were taken from the MARCS database. The standard concept of isotropic Gaussian microturbulence was assumed in this study. A satisfactory fit between the synthesized profiles of spectral lines and observational data verified the reliability of the Fourier method. The most likely estimates of turbulence velocities, the rotation velocity, and the iron abundance and their photospheric depth distribution profiles were obtained as a result. Microturbulence does not vary to any significant degree with depth, while macroturbulence has a marked depth dependence. The macroturbulence velocity increases with depth in the stellar atmosphere. The higher the effective temperature of a star and the stronger the surface gravity, the steeper the expected macroturbulence gradient. The mean macroturbulence velocity increases for stars with higher temperatures, weaker gravity, and faster rotation. The mean macro- and microturbulence velocities are correlated with each other and with the rotation velocity in the examined stars. The ratio between the macroturbulence velocity and the rotation velocity in solar-type stars varies from 1 (the hottest stars) to 1.7 (the coolest stars). The age dependence of the rotation velocity is more pronounced than that of the velocity of macroturbulent motions.

中文翻译：

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太阳型恒星的湍流和自转

摘要

微湍流，大湍流，热运动和旋转有助于拓宽恒星光谱中的线轮廓。在系外行星研究中，需要关于恒星大气中湍流运动速度分布的可靠数据来明确解释太阳型恒星的光谱。通过HARPS光谱仪获得的高分辨率的11.5万颗恒星光谱为检查湍流速度及其在恒星光层中的深度分布提供了机会。对13条恒星光谱中的17条铁谱线进行了傅里叶分析，有效温度为4900-6200 K，表面重力的对数为3.9-5.0，以及太阳光谱中的恒星。恒星大气的模型取自MARCS数据库。本研究假设各向同性高斯微湍流的标准概念。谱线的合成轮廓与观测数据之间的令人满意的拟合证明了傅里叶方法的可靠性。结果，获得了湍流速度，旋转速度，铁丰度及其光球深度分布轮廓的最可能估计。微观湍流不会随深度变化很大，而宏观湍流具有明显的深度依赖性。宏观湍流速度随着恒星大气中深度的增加而增加。恒星的有效温度越高，表面重力越强，预期的大湍流梯度就越陡。对于具有较高温度，较弱重力和较快自转的恒星，平均大湍流速度会增加。平均宏观和微观湍流速度彼此相关，并且与被检查恒星的旋转速度相关。太阳型恒星的大湍流速度与自转速度之比从1（最热的恒星）到1.7（最冷的恒星）不等。旋转速度的年龄依赖性比大湍流运动的速度更加依赖年龄。