Effect of tides on the orbital evolution of the redback system PSR 1723–2837

Abstract

The standard model of stellar evolution in Close Binary Systems assumes that duringmass transfer episodes the system is in a synchronised and circularised state. Remarkably, theredback system PSR J1723-2837 has an orbital period derivative P˙orb too large to be explained by this model. Motivated by this fact, we investigate the action of tidal forces in between twoconsecutive mass transfer episodes for a system under irradiation feedback, which is a plausible progenitor for PSR J1723-2837. We base our analysis on Hut?s treatment of equilibriumtidal evolution, generalised by considering the donor as a two layers object that may not rotate as a rigid body. We also analyse three different relations for the viscosity with the tidal forcingfrequency. We found that the large value measured for Porb can be reached by systems wherethe donor star rotates slower (by few percent) than the orbit just after mass transfer episodes.Van Staden & Antoniadis have observed this object and reported a lack of synchronism, opposite to that required by the Hut?s theory to account for the observed Porb. Motivated by thisdiscrepancy, we analyse photometric data obtained by the spacecraft Kepler second missionK2, with the purpose of identifying the periods present in PSR J1723-2837. We notice severalperiods close to those of the orbit and the rotation. The obtained periods pattern reveals thepresence of a more complex phenomenology, which would not be well described in the frameof the weak friction model of equilibrium tides.