Evolution of W UMa systems and angular momentum loss

Details Evolution of W UMa systems and angular momentum loss Evolution of W UMa systems and angular momentum loss

Sep 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981a%26a...102...81r&link_type=abstract

Astronomy and Astrophysics, vol. 102, no. 1, Sept. 1981, p. 81-90. Research supported by the Finnish Cultural Foundation.

Astronomy and Astrophysics

Astrophysics

74

Angular Momentum, Binary Stars, Momentum Transfer, Stellar Evolution, Colorimetry, Mass Ratios, Stellar Mass, Stellar Models

Scientific paper

The evolution of contact binaries is investigated in order to develop an understanding of the structure and evolutionary state of W UMa stars. The models used are in good thermal contact and have equal entropies in the envelopes. It is assumed that the orbital angular momentum is constant as long as the system has deep contact. As the depth of contact becomes very shallow, the orbital angular momentum is treated as a free parameter, and the system is kept in marginal contact at each time step. A steady loss of angular momentum will drive the system toward smaller mass ratios (Robertson and Eggleton, 1977); evolution toward more extreme mass ratios can be found on the secondary thermal timescale, which becomes longer as the secondary transfers mass to the primary. Mass ratios as extreme as approximately 0.2 have been obtained, and the timescale of the required angular momentum loss is about 5 x 10 to the 8th years. A comparison of the observed periods, mass ratios, and colors of W UMa system with the properties of the mode, shows that the division of W UMa systems into W-type and A-type systems is probably related to the convective or radiative nature of the common envelope at the inner contact surface.

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