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Observational Evidence for Tidal Interaction in Close Binary Systems
Published online by Cambridge University Press: 20 June 2008
Abstract
This paper reviews the rich corpus of observational evidence for tidaleffects, mostly based on photometric and radial-velocity measurements.This is done in a period when the study of binaries is beingrevolutionized by large-scaled photometric surveys that are detectingmany thousands of new binaries and tens of extrasolar planets. We begin by examining the short-term effects, such as ellipsoidalvariability and apsidal motion. We next turn to the long-termeffects, of which circularization was studied the most: a transitionperiod between circular and eccentric orbits has been derived foreight coeval samples of binaries. The study of synchronization andspin-orbit alignment is less advanced. As binaries are supposed toreach synchronization before circularization, one can expect findingeccentric binaries in pseudo-synchronization state, the evidence forwhich is reviewed. We also discuss synchronization in PMS and youngstars, and compare the emerging timescale with the circularizationtimescale. We next examine the tidal interaction in close binaries that areorbited by a third distant companion, and review the effect ofpumping the binary eccentricity by the third star. We elaborate on theimpact of the pumped eccentricity on the tidal evolution of closebinaries residing in triple systems, which may shrink the binary separation. Finally we consider the extrasolar planets and the observationalevidence for tidal interaction with their parent stars. This includesa mechanism that can induce radial drift of short-period planets,either inward or outward, depending on the planetary radial positionrelative to the corotation radius. Another effect is thecircularization of planetary orbits, the evidence for which can befound in eccentricity-versus-period plot of the planets already known. Whenever possible, the paper attempts to address the possibleconfrontation between theory and observations, and to point outnoteworthy cases and observations that can be performed in the futureand may shed some light on the key questions that remain open.
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- © EAS, EDP Sciences, 2008
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