The Occurrence Rate of Nearby Planetary Companions to Hot Jupiters

TL;DR

This study estimates that about 7.6% of hot Jupiters have nearby companions, suggesting most hot Jupiters likely formed through disk migration or in situ processes, with implications for their formation history.

Contribution

The paper provides a uniform occurrence rate of nearby companions to hot Jupiters using TESS data, constraining hot Jupiter formation pathways and their orbital alignments.

Findings

Approximately 7.6% of hot Jupiters have nearby companions.

Hot Jupiters with companions are likely aligned with them.

Evidence suggests hot Jupiters with companions may also have cold companions.

Abstract

Of the > 500 confirmed transiting hot jupiters and approximately 2000 additional candidates today, only ten are known to have nearby companion planets. The survival of nearby companions means that these hot jupiters cannot have migrated to their present location via dynamically disruptive high-eccentricity migration but instead have undergone disk migration or formed in situ. The occurrence rate for these nearby companions, therefore, constrains the relative efficiency of different hot jupiter formation pathways. Here, we perform a uniform box least-squares search for nearby transiting companions to hot jupiters in the first five years of TESS data. Accounting for observational completeness and detection efficiency, we arrive at an occurrence rate of $(7.6^{+5.5}_{-3.8})\%$, which is a lower limit on the fraction of hot jupiters that underwent disk migration or in situ formation. Comparing this rate with that derived from transit-timing variation searches suggests that hot jupiters are likely mostly aligned with their nearby companions, but their apparently higher incidence of grazing transits may point to a slight preferential misalignment. We also synthesize evidence that hot jupiters with nearby companions may have cold companions at a rate similar to that of other hot jupiters. Comprehensive transit, radial velocity, and stellar obliquity measurements in hot jupiter systems with nearby companions will be necessary to fully account for the relative prevalence of proposed hot jupiter formation pathways.