Giant planet occurrence within 0.2 AU of low-luminosity red giant branch stars with K2

TL;DR

This study estimates the occurrence of close-in giant planets around low-luminosity red giant branch stars using K2 data, finding a potentially higher occurrence rate compared to Sun-like stars, with implications for planetary evolution during stellar aging.

Contribution

It provides the first statistical estimate of giant planet occurrence within 0.2 AU of LLRGB stars, utilizing asteroseismology for precise stellar characterization and comparing with main sequence star populations.

Findings

0.51% of LLRGB stars host close-in giant planets.

Potentially higher occurrence rate than around Sun-like stars.

Stellar evolution effects on close-in giant planets are minimal until advanced red giant stages.

Abstract

Every Sun-like star will eventually evolve into a red giant, a transition which can profoundly affect the evolution of a surrounding planetary system. The timescale of dynamical planet evolution and orbital decay has important implications for planetary habitability, as well as post-main sequence star and planet interaction, evolution and internal structure. Here, we investigate these effects by estimating planet occurrence around 2476 low-luminosity red giant branch (LLRGB) stars observed by the NASA K2 mission. We measure stellar masses and radii using asteroseismology, with median random uncertainties of 3.7% in mass and 2.2% in radius. We compare this planet population to the known population of planets around dwarf Sun-like stars, accounting for detection efficiency differences between the stellar populations. We find that 0.51% +/- 0.29% of LLRGB stars host planets larger than Jupiter with orbital periods less than 10 days, tentatively higher than main sequence stars hosting similar planets (0.15% +/- 0.06%). Our results suggest that the effects of stellar evolution on the occurrence of close-in planets larger than Jupiter is not significant until stars have begun ascending substantially up the red giant branch (>~ 5-6 Rsun).