Relationship between the Velocity Ellipsoids of Galactic-Disk Stars and their Ages and Metallicities - Astrophysics > Astrophysics of GalaxiesReport as inadecuate




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Abstract: The dependences of the velocity ellipsoids of F-G stars of the thin disk ofthe Galaxy on their ages and metallicities are analyzed based on the newversion of the Geneva-Copenhagen Catalog. The age dependences of the major,middle, and minor axes of the ellipsoids, and also of the dispersion of thetotal residual veltocity, obey power laws with indices 0.25,0.29,0.32, and 0.27with uncertainties \pm 0.02. Due to the presence of thick-disk objects, theanalogous indices for all nearby stars are about a factor of 1.5 larger.Attempts to explain such values are usually based on modeling relaxationprocesses in the Galactic disk. With increasing age, the velocity ellipsoidincreases in size and becomes appreciably more spherical, turns toward thedirection of the Galactic center, and loses angular momentum. The shape of thevelocity ellipsoid remains far from equilibrium. With increasing metallicity,the velocity ellipsoid for stars of mixed age increases in size, displays aweak tendency to become more spherical, and turns toward the direction of theGalactic center with these changes occurring substantially more rapidly in thetransition through the metallicity Fe-H= -0.25. Thus, the ellipsoid changessimilarly to the way it does with age; however, with decreasing metallicity,the rotational velocity about the Galactic center monotonically increases,rather than decreases!. Moreover, the power-law indices for the agedependences of the axes depend on the metallicity, and display a maximum nearFe-H=-0.1. The age dependences of all the velocity-ellipsoid parameters forstars with equal metallicity are roughly the same. It is proposed that theappearance of a metallicity dependence of the velocity ellipsoids for thin-diskstars is most likely due to the radial migration of stars.



Author: V.V.Koval', V.A.Marsakov, T.V.Borkova

Source: https://arxiv.org/







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