The long-term evolution of photoevaporating transition discs with giant planets

Abstract

Photo-evaporation and planet formation have both been proposed as mechanisms responsible for the creation of a transition disc. We have studied their combined effect through a suite of 2d simulations of protoplanetary discs undergoing X-ray photoevaporation with an embedded giant planet. In a previous work we explored how the formation of a giant planet triggers the dispersal of the inner disc by photo-evaporation at earlier times than what would have happened otherwise. This is particularly relevant for the observed transition discs with large holes and high mass accretion rates that cannot be explained by photo-evaporation alone. In this work we significantly expand the parameter space investigated by previous simulations. In addition, the updated model includes thermal sweeping, needed for studying the complete dispersal of the disc. After the removal of the inner disc the disc is a non accreting transition disc, an object that is rarely seen in observations. We assess the relative length of this phase, to understand if it is long lived enough to be found observationally. Depending on the parameters, especially on the X-ray luminosity of the star, we find that the fraction of time spent as a non-accretor greatly varies. We build a population synthesis model to compare with observations and find that in general thermal sweeping is not effective enough to destroy the outer disc, leaving many transition discs in a relatively long lived phase with a gas free hole, at odds with observations. We discuss the implications for transition disc evolution. In particular, we highlight the current lack of explanation for the missing non-accreting transition discs with large holes, which is a serious issue in the planet hypothesis.

Constraining planet formation around 6–8 M⊙ stars

“…These planets formed in discs which are subject to time-varying radiative forcing at a more extreme level than their lower-host mass counterparts. When combined with photoevaporative effects from other stars in their birth cluster, outward migration of planets within these discs may be enhanced (Veras & Armitage 2004;Rosotti et al 2013Rosotti et al , 2015Jennings et al 2018). If the 6M⊙ − 8M⊙ progenitor host stars for polluted white dwarfs were slightly more massive, then they would have instead become neutron stars; planets are known to exist around single pulsars (Wolszczan & Frail 1992;Wolszczan 1994;Konacki & Wolszczan 2003).…”

Photoevaporation Does Not Create a Pileup of Giant Planets at 1 au

“…Though we use an axisymmetric prescription for photoevaporative mass lossΣ pe (r), the relative surface density change induced by photoevaporation can be very high for the non-axisymmetric tidal tails and co-rotating horseshoe in the planet's tidal gap because of their low densities compared to the surrounding disk. Simulations of giant planets migrating in 2-D photoevaporating disks have been performed using FARGO in previous studies (Moeckel & Armitage 2012;Rosotti et al 2013Rosotti et al , 2015. Moeckel & Armitage (2012) study how planet orbital distributions from planetplanet scattering evolve during the gas disk phase and the n-body phase after the gaseous disk is dispersed by photoevaporation.…”

The Origin and Evolution of Transition Discs: Successes, Problems, and Open Questions

“…Rosotti et al (2013Rosotti et al ( , 2015 studied the impact of photoevaporation on a disc with an embedded planet. The result of including a planet was that photoevaporative clearing of the inner disc was triggered early (as the planet helps starve the inner disc while the planet was at large radius).…”