Abstract
We show that the observed decline in the orbital period of the merger candidate V1309 Sco could have been driven by tidal shear energy dissipation, dotE_S. This mechanism becomes relevant once the expanding layers of an evolving star rotate asynchronously. For a 1 M_⊙+0.8 M_⊙ system with orbital period P=1.44 d, we find that dotE_S can power a growth in stellar radius from 1.50 R_⊙ to 1.85 R_⊙ in the primary over the course of ≃ 5 years, during which the rate of period change goes from ≃ 1000 yr to ≃ 170 yr, in agreement with the observations. The kinematical viscosity used for these calculations is estimated from the maximum tidal flow speed and from the extension of the the tidal bulge, and is thus a function of the stellar and orbital parameters.
