Observational Signatures of Circumstellar Gas Tori Formed by Planetary Mass-Loss from Close-In Exoplanets

TL;DR

This paper models circumstellar gas tori formed by planetary mass-loss in close-in exoplanets, showing they can be detected via specific spectral line enhancements, aiding the identification of such systems.

Contribution

It introduces a physical model and ray tracing method to predict spectral signatures of circumstellar tori caused by planetary mass-loss, proposing a new observational survey approach.

Findings

Circumstellar tori increase the He I 10830 Å line's equivalent width.

Combined He I and Ca II line observations can distinguish these systems from field stars.

The model provides a basis for targeted observational searches for planetary mass-loss signatures.

Abstract

Close-in exoplanets with H/He atmospheres often undergo hydrodynamic escape. In extreme cases, it is hypothesized that the mass loss can be high enough for the escaping planetary material to wrap around the star, forming a long-lasting circumstellar torus. In this work, we develop a physical model of such circumstellar tori and use a ray tracing scheme to calculate the attenuation of stellar light passing through them. We show that the presence of a circumstellar torus significantly increases the equivalent width of the observed stellar He I 10830~\AA~line. When combined with observations of the star's Ca II H & K lines, these systems can typically be distinguished from field stars. Based on these results, we propose a survey of stars hosting close-in planets, combining observations of the He I 10830~\AA~and Ca II H & K lines to search for circumstellar tori generated from planetary mass-loss in these systems.