Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997a%26a...318..187c&link_type=abstract
Astronomy and Astrophysics, v.318, p.187-197
Astronomy and Astrophysics
Astrophysics
89
Stars: Binaries: Close, Evolution, Rotation
Scientific paper
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 λ_2_ and E_2_ 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 1995A&AS..109..441C, 1997, A&AS submitted; Claret & Gimenez 1995A&A...296..180C, 1995A&AS..114..549C). 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/t_cri_) x 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 x 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.
Claret Antonio
Cunha C. S. N.
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