Turbulence and rotation in solar-type stars

1Sheminova, VA
1Main Astronomical Observatory of the National Academy of Sciences of Ukraine, Kyiv, Ukraine
Kinemat. fiz. nebesnyh tel (Online) 2019, 35(3):44-66
Start Page: Physics of Stars and Interstellar Medium
Language: Russian

Microturbulence, macroturbulence, rotation along with thermal motions expand the profiles of lines in stellar spectra. Reliable data on the velocity distribution of turbulent motions in stellar atmospheres are necessary to perform an unambiguous interpretation of the spectra of solar-type stars in studies and searches for exoplanets. Stellar spectra with a high spectral resolution of 115 000 obtained with the HARPS spectrograph make it possible to investigate the turbulent velocities and their dependencies with depth in the photosphere of stars. We performed Fourier analysis for 17 iron lines in the spectra of 13 stars with effective temperatures of 4900...6200 K and the gravity of 3.9...5.0, as well as in the spectrum of the Sun as stars. Models of star atmospheres were taken from the MARCS database. The standard concept of isotropic Gaussian microturbulence was assumed in this analysis. The satisfactory fit of the synthesized profiles of spectral lines with observations confirmed the reliability of the Fourier method. As a result, we obtained the most probable values of the turbulent velocities, the rotation velocity, the iron abundance and their dependencies with depth in the photosphere layers. Microturbulence does not show a significant dependence with depth, while macroturbulence clearly depends on depth. The macroturbulent velocity grows with depth in the photospheres of stars. The greater the effective temperature of the star and the greater of gravity, the greater the gradient of macroturbulence can be expected. The average value of the macroturbulent velocity increases for stars with higher temperatures, less graviy and faster rotation. In the stars analyzed, the average velocity of macroturbulence and microturbulence correlate with each other and with the rotation velocity. The relationship between the macroturbulence velocity and the rotational velocity varies from 1 to 1.7 from the hottest to the coldest solar-type stars. With the age of the star, the rotational velocity decreases more sharply than the velocity of macroturbulent motions.

Keywords: Fourier method, iron abundance, line profiles, rotation, solar-type stars, velocity field

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