Evolution of Circumbinary Protoplanetary Disks with Photoevaporative Winds Driven by External Far-ultraviolet Radiation

Lifetimes of protoplanetary disks (PPDs) are believed to be severely constrained by material-depleting mechanisms, including photoevaporative winds due to the host star radiation or external radiation sources. Most previous studies focused on exploring the role of the winds in the exposed PPDs with a single star; however, the evolution of the circumbinary disks with the photoevaporative winds driven by the host star radiation and external radiation sources deserves further exploration. In this study, we investigate the evolution of the circumbinary PPDs with the photoevaporative winds induced by the external far-ultraviolet radiation field. We show that this mass-loss process can significantly constrain properties of a circumbinary PPD, including its lifetime, mass, and radius. The lifetime of a circumbinary PPD, for instance, is found to be about a factor of two longer than a similar circumstellar disk, and this enhancement strongly depends on the viscosity parameter. But our model shows that viscosity dependence of the disk lifetime in the circumbinary case is more pronounced compared to the circumstellar case. We also show that dispersal of a circumbinary PPD occurs over a longer time as the disk temperature distribution becomes steeper. Our results also imply that a dead zone in a photoevaporative circumbinary PPD extends over a larger radial range in comparison to a circumstellar disk counterpart. We also show that our calculations are in agreement with the observed circumbinary PPDs orbiting equal-mass binaries.