\journalname
Astronomy&AstrophysicsReview

Tidal evolution and apsidal motion

\label{apsidal}
Well-detached binaries with accurate absolute dimensions provide excellent data with which to study the dynamical effects of tidal friction as well as to explore the internal stellar structure. Tidal evolution is observed by measuring the degree of circularisation of the orbit and the level of synchronisation of the rotational velocities, being a very active field with discussions on alternative theories for the physical description of tidal friction \citep[see, e.g.,][and references therein]{mazeh}.
Internal structure constants \(\log k_{2}\) are indicative of the degree of central density concentration of the component stars and can be observed in eccentric systems by measuring the apsidal motion period \citep[e.g.,][]{2007IAUS..240..290G}. In Table \ref{tableaps} we list all systems from Table \ref{tableMR} with eccentric orbits, as well as those with measured apsidal rates d\(\omega\)/dt. References are given for the apsidal motion determinations. In three cases (EW Ori, V459 Cas, and MY Cyg), the original values were corrected to an adopted eccentricity consistent with the photometric and spectroscopic studies. Here we do not attempt to perform a detailed analysis of the individual systems in this table, but rather to provide a high-quality database satisfying the adopted selection criteria, allowing such studies, including the confrontation with stellar evolution models.

Tidal circularisation and synchronisation

\label{tidalevol}
Our sample of detached binaries contains both circular and eccentric orbits; in fact, 44 of the 95 systems are eccentric. The left-hand panels of Fig. \ref{tidal} show the distribution of orbital eccentricity as a function of orbital period, separately for stars with radiative and convective envelopes, adopting \(T_{\rm eff}=7000\) K as the limit between the two groups. For clarity, the two longest-period systems, \(\alpha\) Cen and OGLE 051019, are not shown.
Observational biases limit the sample to orbital periods mostly below 10 days. The special case of TZ For, with two evolved stars in a circular orbit of period 75.7 days, was explained in detail by \cite{1995A+A...296..180C}, who integrated the circularisation time scales along the evolution of the component stars. The only other longer-period system in this diagram, AI Phe (24.6 days), shows an eccentric orbit, but with synchronised rotational velocities.