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Astron. Astrophys. 318, 187-197 (1997)


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Circularization and synchronization times in Main-Sequence of detached eclipsing binaries

II. Using the formalisms by Zahn

A. Claret 1 and N.C.S. Cunha 2

1 Instituto de Astrofísica de Andalucía, CSIC, Apartado 3004, E-18080 Granada, Spain
2 Laboratorio de Astrofísica Espacial y Física Fundamental, INTA, Apartado 50727, E-28080 Madrid, Spain

Received 27 November 1995 / Accepted 2 July 1996

Abstract

Double-lined eclipsing binaries with accurate absolute dimensions are the best stellar data to test tidal evolution theories due to the high dependency of the time scales on masses, relative radii and periods. In a preceding paper we have probed the hydrodynamical mechanism against the observed levels of synchronization and circularization for about 40 close binary systems with accurate absolute dimensions. In the present work we extend our investigations, using the same systems as a control, to the turbulent dissipation and radiative damping mechanisms which have been studied by Zahn. The time scales for these processes are characterized by the parameters [FORMULA] and E2 respectively. These parameters were computed for a wide grid of stellar models and they are presented, for the first time, as functions of the mass and time.

The differential equations which govern the orbital parameters were integrated using our recent grids of stellar models (Claret 1995,1996 ; Claret & Giménez 1995). The derived critical times and radii were compared with observations of synchronization and circularization levels. Within uncertainties, the formalisms by Zahn seem to be able to explain the eccentricity distribution around the zero point of the diagram log (age/ [FORMULA]) [FORMULA] eccentricity although they can not explain some systems with circular orbits which present ages smaller than their respective critical times.

We have also introduced a diagram based on the integration of the differential equations which proved to be useful to test theoretical predictions for the relationship age [FORMULA] Period (cut-off) for clusters. Using this diagram we have shown that the turbulent friction mechanism is not dissipative enough to explain such an observational relationship. However, as these results are valid only for little departure from synchronism and small eccentricity, we plan to investigate the influence of the initial conditions in a forthcoming paper.

Key words: stars: binaries: close; evolution; rotation

Send offprint requests to: A. Claret (claret@iaa.es)

© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998

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