an aggregate of all stars (or other objects) of a certain spectral class or type which forms part of the Milky Way Galaxy and is distinguished by the individual characteristics of its location in space and peculiarities in the velocity distribution of the stars. Star clusters and interstellar gas and dust also form subsystems of our galaxy.
Each stellar subsystem is characterized by the type and number of objects in it and the degree of concentration of the objects toward the galaxy’s center and plane of symmetry. Objects that have a high concentration toward the galaxy’s plane of symmetry form stellar subsystems belonging to the flat component of the Milky Way Galaxy. They include hot giants and supergiants of spectral classes O and B, long-period cepheids, Population type II supernovas, open clusters, and dust and gas matter. In the flat component the concentration of objects toward the center of the galaxy is very low. Objects that have a low concentration toward the galaxy’s plane of symmetry constitute stellar subsystems belonging to the galaxy’s spherical component. Such objects include subdwarfs, short-period cepheids, long-period variables with a period of brightness varying from 150 to 200 days, and globular clusters. Stellar subsystems of the spherical component have a strong concentration toward the galaxy’s center. Stellar subsystems of the intermediate component are formed by objects that have moderate concentration toward the galaxy’s plane of symmetry. They include red dwarfs, novas, Population type I supernovas, RV Tauri variables, and planetary nebulas.
In accordance with the conclusions of dynamics, the flattening of each subsystem is connected with the average value of the velocity component perpendicular to the galactic plane. The flat component must possess the smallest velocity component (since otherwise the objects of the subsystem would recede to great distances from the galactic plane and the subsystem could not be flat) and the spherical component the largest. Observations confirm the presence of such a relation.
Essential differences in the structure of subsystems of various objects must be the result of different conditions of formation of these objects, in particular the result of their formation at different stages in our galaxy’s evolution. The concept of the Milky Way Galaxy as an aggregate of interpenetrating subsystems was developed by the Soviet astronomers P. P. Parenago, B. V. Kukarkin, and others. The existence of stellar subsystems has also been discovered in several other galaxies. Stellar subsystems are investigated in stellar astronomy.
T. A. AGEKIAN