EDP Sciences
Free access
Volume 395, Number 3, December I 2002
Page(s) 907 - 913
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20021338

A&A 395, 907-913 (2002)
DOI: 10.1051/0004-6361:20021338

On the structure of contact binaries

H. Kähler

Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
(Received 3 April 2002 / Accepted 13 September 2002)

In a preceding paper a simple model for contact binaries has been proposed, based on the usual assumption that the energy sources/sinks caused by the interaction of the components occur only in the secondary's/primary's outer layers. Here the model is applied to a typical late-type system.

First we imposed the restriction that the fractional extent in mass of the sources/sinks in the layers above the critical surface is the same in both components, and found solutions evolving in thermal cycles. If the energy transfer is assumed to be sufficiently effective, loss of contact is avoided. Otherwise the cycle consists of a long quiet phase in good contact and a short violent phase with rapid changes between contact, semidetached, and detached configurations. In both cases there are cycles in which the temperatures of the components are similar in the largest part of the time. Other observational tests are also passed.

Next we removed the restriction. In the resulting model with three free parameters we found (besides cycles) a large range of solutions in stable thermal equilibrium which are compatible with the observations.

From a theoretical viewpoint however all these solutions are unsatisfactory since suffering from several inconsistencies. This result shows that the usual assumption on the energy sources and sinks is too restrictive. We are led to look for modifications of the model which remove the inconsistencies. This will be done in a forthcoming paper.

Key words: stars: binaries: close

© ESO 2002