Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982a%26a...111....1o&link_type=abstract
Astronomy and Astrophysics, vol. 111, no. 1, July 1982, p. 1-27.
Astronomy and Astrophysics
Astrophysics
21
Binary Stars, Galactic Nuclei, Globular Clusters, Stellar Evolution, Stellar Systems, Energy Dissipation, Energy Transfer, Kinetic Energy, Mass Transfer, Stellar Temperature
Scientific paper
We consider here the main processes leading to the formation of hard binaries in a collisionless stellar system, i. e. of binaries whose binding energy exceeds the mean kinetic energy of stars in the system. It is assumed that initially there are no binaries. The formation rate of hard binaries by means of unbound stars (this process was well studied earlier) is compared with the detailed calculations of hard binary formation due to tidal self-hardening of soft pairs. The latter are formed as a result of two processes: (i) at (dissipative) two-body encounters of single stars and (ii) at (dissipationless) three-body encounters. It is shown that in large stellar systems such as globular clusters and galactic nuclei, the rate of the tidal self-hardening of soft binaries formed in the process (i) is much higher than that in the process (ii).
Further, we analyze both the energy dissipation from a stellar system due to the formation there of bound pairs and the heating of the system due to the hardening of hard binaries in the course of their encounters with single stars (this hardening becomes essential only after the completion of the tidal circularization of the binary orbits). In stellar systems with parameters of typical globular clusters, the energy dissipation due to tidal interactions of single stars predominates over the heating due to hardening of hard binaries; the smallness of the heating is conditioned by the fact that the newly formed binaries, after circularization of their orbits, become too hard. In stellar systems with the parameters of typical galactic nuclei, hard binaries formed appear to be too close but after the tidal outflow of matter from one component of a binary onto another and after the subsequent transformation of the latter into a white dwarf or a neutron star they are capable of further hardening. A factor limiting the accompanying heating of a nucleus by hard binaries is their gravitational radiation. Conditions are found under which the heating by hard binaries in galactic nuclei can predominate over the dissipative cooling.
The rates of cooling and heating of a stellar system by binaries given in the present paper form a necessary basis for the investigation of the influence of binaries on the evolution of stellar systems which is considered in the second paper of this series.
Dokuchaev Viacheslav I.
Ozernoi L. M.
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