Bibcode
Cunha, N. C. S.; Gimenez, A.; Claret, A.
Bibliographical reference
Astronomy and Astrophysics, v.299, p.724
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7
1995
Journal
Citations
93
Refereed citations
83
Description
We have studied a sample of selected eclipsing binaries with eccentric
orbits and accurate absolute dimensions in order to analyse the validity
of available theories of tidal evolution concerning synchronization and
circularization time scales. In the present investigation we pay special
attention to stars with radiative envelopes though some stars with outer
layers in convective equilibrium have been included to show different
aspects of tidal evolution. In the present paper, we have adopted for
the comparison with observational parameters, the tidal theory by
Tasssoul (1987, 1988). The formalism introduced by Zahn (1977, 1989)
will be the subject of a separate paper. The critical values of the age,
log g and R for circularization and synchronization have been computed
using a set of stellar models which include recent opacity libraries,
core overshooting and mass loss. These values can be computed as a
function of the orbital period for different masses. In this way, it is
relatively simple to compare them with observational values and,
therefore, to analyse the behaviour of parameters which indicate the
actual situation, namely, the eccentricity and the rotational
velocities. The comparison of observed rotational velocities with
expected values for each binary system configuration has shown that
nearly all systems in our sample are actually pseudo-synchronized with
their orbital periods (i.e. with the fastest orbital velocity in
eccentric systems) in good agreement with theoretical predictions. These
results, however, should be taken with some caution since the rotation
of the stellar interior may be decoupled from that of the surface
layers. With respect to circularization, a cutoff value around log t=log
t_cri_(or log g_obs_=log g_cri_) shows a satisfactory agreement for
observational values of the eccentricity. Furthermore, we concluded that
the circularization process is still active during the main sequence
stage for early-type binaries.