Observational signatures of circumstellar gas tori formed by planetary mass-loss from close-in exoplanets

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 Å line. When combined with observations of the star’s Ca ii H and 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 Å and Ca ii H and K lines to search for circumstellar tori generated from planetary mass-loss in these systems.