Planet Engulfment Detections are Rare According to Observations and Stellar Modeling

TL;DR

This study investigates the rarity of planet engulfment signatures in multi-star systems through observations and stellar modeling, finding such events are infrequent and short-lived, especially in older stars.

Contribution

It combines a Keck-HIRES survey of multi-star systems with stellar models to assess the detectability and frequency of planetary engulfment signatures.

Findings

Engulfment signatures last about 90 Myr in 1 solar mass stars.

Only one system showed potential signs of engulfment, likely primordial.

Detectable signatures are rare in systems older than 2 Gyr.

Abstract

Dynamical evolution within planetary systems can cause planets to be engulfed by their host stars. Following engulfment, the stellar photosphere abundance pattern will reflect accretion of rocky material from planets. Multi-star systems are excellent environments to search for such abundance trends because stellar companions form from the same natal gas cloud and are thus expected to share primordial chemical compositions to within 0.03$-$0.05 dex. Abundance measurements have occasionally yielded rocky enhancements, but few observations targeted known planetary systems. To address this gap, we carried out a Keck-HIRES survey of 36 multi-star systems where at least one star is a known planet host. We found that only HAT-P-4 exhibits an abundance pattern suggestive of engulfment, but is more likely primordial based on its large projected separation (30,000 $\pm$ 140 AU) that exceeds typical turbulence scales in molecular clouds. To understand the lack of engulfment detections among our systems, we quantified the strength and duration of refractory enrichments in stellar photospheres using MESA stellar models. We found that observable signatures from 10 $M_{\oplus}$ engulfment events last for $\sim$90 Myr in 1 $M_{\odot}$ stars. Signatures are largest and longest lived for 1.1$-$1.2 $M_{\odot}$ stars, but are no longer observable $\sim$2 Gyr post-engulfment. This indicates that engulfment will rarely be detected in systems that are several Gyr old.