Are Stars Really Ingesting their Planets? Examining an Alternative Explanation

TL;DR

This study suggests that variations in stellar refractory element abundances, often attributed to planetary ingestion, can also result from dust-to-gas ratio differences during star formation, as shown by advanced simulations.

Contribution

It introduces a novel explanation for abundance variations, emphasizing dust physics and dynamics as alternative causes to planetary ingestion.

Findings

10-30% of stars show abundance variations around 0.1 dex.

Variations are comparable to accreting 2-5 Earth masses of planetary material.

No correlation between abundance variations and stellar separation.

Abstract

Numerous stars exhibit surprisingly large variations in their refractory element abundances, often interpreted as signatures of planetary ingestion events. In this study, we propose that differences in the dust-to-gas ratio near stars during their formation can produce similar observational signals. We investigate this hypothesis using a suite of radiation-dust-magnetohydrodynamic STARFORGE simulations of star formation. Our results show that the distribution of refractory abundance variations ($\rm \Delta [X/H]$) has extended tails, with about 10-30% of all stars displaying variations around $\sim$0.1 dex. These variations are comparable to the accretion of $2-5 \rm M_\oplus$ of planetary material into the convective zones of Sun-like stars. The width of the distributions increases with the incorporation of more detailed dust physics, such as radiation pressure and back-reaction forces, as well as with larger dust grain sizes and finer resolutions. Furthermore, our simulations reveal no correlation between $\rm \Delta [X/H]$ and stellar separations, suggesting that dust-to-gas fluctuations likely occur on scales smaller than those of wide binaries. These findings highlight the importance of considering dust dynamics as a potential source of the observed chemical enrichment in stars.