Description:

Title: Investigating the Role of Stellar Tides in Hot Jupiter's Origin and Fate

Speaker: Francesca Valsecchi, Northwestern University

Abstract: Two formation models have been proposed to explain hot Jupiters’ tight orbits. These could have migrated inward in a disk (disk migration), or they could have formed via tidal circularization of an orbit made highly eccentric following gravitational interactions with a companion (high-eccentricity migration). Disk migration drives hot Jupiters down to their Roche limit separations a_R, in orbits where the stellar spin and orbital angular momentum vectors are nearly aligned. High-eccentricity migration results in an inner cutoff at 2a_R and in a broad range of misalignments. Using state-of-the-art stellar models and a detailed treatment of tidal dissipation, we show that currently observed systems are consistent with high-eccentricity migration. In this scenario, stellar tides shaped the observed distribution of misalignments, and brought inward from beyond 2a_R the currently known hot Jupiters that lie within 2a_R. Interestingly, this population potentially provides direct empirical constraints on tidal dissipation theories.
Eventually, stellar tides will cause the orbits of many hot Jupiters to decay down to a_R. Using a standard binary mass transfer model we show how a hot Jupiter undergoing a phase of Roche-lobe overflow (RLO) leads to a hot super-Earth in an orbit of few hours to several days. This model predicts planets with intermediate masses (``hot Neptunes'') that should be found in the process of losing mass through RLO. The observed excess of small single-planet candidate systems observed by Kepler may also be the result of this process. If so, the number of systems that produced hot Jupiters could be 2-3 times larger than one would infer from contemporary observations.

Keywords: Physics, Astronomy, Astrophysics