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0220U103579,
0117U004968
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The method of Vector Spherical Harmonics for kinematic investigations of our Galaxy based on space and ground data.
Ahmetov Volodymir S., Кандидат фізико-математичних наук
22-10-2020
V.N. Karazin Kharkiv National University
The aim of the fourth final stage of the project is a comprehensive study of the kinematic parameters of the Galaxy obtained using data GaiaDR2 and PMA catalogues on based modern physical models and on the velocity field decomposition by Vector Spherical Harmonic (VSH). All stars at distances up to 1 kps were divided into samples according to the color index and for each sample the kinematic parameters were obtained as by mean of to the Ogorodnikov-Milna model and also VSH. When analyzing the velocity field separately in the northern and southern galactic hemispheres, we can directly calculate the value of the vertical gradient dVrot/dz. According to the stellar proper motions of Gaia DR2 and PMA catalogues, it was found that stars of early spectral classes, 0.0m<(J-KS)0<0.2m, have a zero vertical gradient. Then it increases with increasing <(J-KS)0 and reaches a value of about 20 km/c/kpc at 0.3m<(J-KS)0<0.4m and then is approximately at this level. It is shown that the parameter ω1 is positive in the northern hemisphere and negative in the southern hemisphere, while M+23, on the contrary, is negative in the northern hemisphere and positive in the southern hemisphere. This means that the vertical gradient, being a linear combination of these two parameters, is negative in the northern hemisphere and positive in the southern. This behavior is due to a decrease in the speed of rotation of the stars around the center of the Galaxy at a distance from its plane. Therefore, we can conclude that the values of Y☉ obtained from the natural motions of the Gaia DR2 and PMA catalog stars are a combination of two effects: the asymmetric drift of stars directly in the plane of the Galaxy and the vertical velocity gradient of the Galaxy. The existence of coefficients t211 is fully explained by the vertical gradient, while the values of s310, in addition to the vertical gradient, may contain the contribution of other effects. The simulation showed that the simultaneous presence
Akhmetov Volodymyr S
Velychko Hanna B
Khlamov Serhii V
Khramtsov Vladyslav P
2021-03-17
Updated: 2026-01-07
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