Physical and Chemical Properties of Galactic Global Clusters with Various Origins Identified from the Gaia DR2 Data
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ical and Chemical Properties of Galactic Global Clusters with Various Origins Identified from the Gaia DR2 Data V. A. Marsakova, *, V. V. Koval’a, **, and M. L. Gozhaa, *** a
Southern Federal University, Rostov-on-Don, 344006 Russia *e-mail: [email protected] **e-mail: [email protected] ***e-mail: [email protected]
Received April 20, 2020; revised June 8, 2020; accepted June 30, 2020
Abstract—The differences in the relationships between the physical parameters and the chemical-element abundances in accreted globular star clusters and those formed inside the Galaxy have been investigated. The information on the supposed formation sites of the clusters based on the Gaia DR2 data is borrowed from the literature. Those sources estimate the probability of belonging to the Galactic bulge and disk, as well as to six known events of the merger of dwarf satellite galaxies with the Milky Way, for 151 globular clusters. Orbital elements, initial masses, population types, and ages are taken from the literature; the data on the chemical composition for 69 globular clusters of the Galaxy are taken from the authors’ compiled catalog. It is shown that all metal-poor ([Fe/H] < −1.0 ) genetically related globular clusters have high relative abundances of α -elements. According to modern views, since type II supernovae release more α -elements into the interstellar medium with increasing mass, it has been suggested that masses of type II supernovae in the Galaxy were greater than in the accreted galaxies. It is proved that the clusters of the low-energy group, which were considered accreted, are genetically related to a single protogalactic cloud, same as the unstratified clusters UKS 1 and Liller 1, which most likely belong to the bulge. It is shown that not only the lower but also the upper limits of the clusters’ masses decrease with an increase in the average radius of their orbits. The latter fact is explained by a decrease in the masses of emerging clusters with a decrease in the masses of their host galaxies. It is demonstrated that an extremely multicomponent stellar population is observed only in accreted globular clusters with an initial mass >10 6 M . It has been suggested that these clusters retained all the matter ejected by their evolved stars, from which new generations of stars formed due to long evolution far from our Galaxy. DOI: 10.1134/S1063772920110062
1. INTRODUCTION According to the modern standard cosmological model ΛCDM (Lambda-Cold Dark Matter), the masses of galaxies grow due to mergers. The galactic halo forms as a result of several large mergers, accompanied by numerous small ones. When satellites merge with a galaxy like the Milky Way, they lose their stars due to tidal forces. These stars follow approximately the mean orbit of their progenitor, and this leads to stream formation. In recent years, observational astronomy has provided us with some compelling evidence that not all stars that currently belong to our Galaxy formed from the same protogalactic cloud. Some stellar objects were captured fr
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