Hot Stars with Hot Jupiters Have High Obliquities

TL;DR

The paper finds that hot stars with hot Jupiters tend to have high obliquities, suggesting different formation or realignment processes compared to cooler stars, impacting theories of planetary migration.

Contribution

It demonstrates a correlation between stellar temperature and obliquity in hot Jupiter systems, proposing a new explanation involving stellar realignment mechanisms.

Findings

Hot stars with hot Jupiters have high obliquities.

Cool stars tend to have aligned planetary orbits.

The realignment process depends on stellar convective zones.

Abstract

We show that stars with transiting planets for which the stellar obliquity is large are preferentially hot (T_eff > 6250 K). This could explain why small obliquities were observed in the earliest measurements, which focused on relatively cool stars drawn from Doppler surveys, as opposed to hotter stars that emerged later from transit surveys. The observed trend could be due to differences in planet formation and migration around stars of varying mass. Alternatively, we speculate that hot-Jupiter systems begin with a wide range of obliquities, but the photospheres of cool stars realign with the orbits due to tidal dissipation in their convective zones, while hot stars cannot realign because of their thinner convective zones. This in turn would suggest that hot Jupiters originate from few-body gravitational dynamics, and that disk migration plays at most a supporting role.