Resonant structures in exozodiacal clouds created by exo-Earths in the habitable zone of late-type stars

TL;DR

This study investigates how resonant structures in exozodiacal dust caused by Earth-like exoplanets vary across different stellar types, emphasizing the significant role of stellar wind drag especially around M-type stars.

Contribution

It extends previous models by including spectral type variation in stellar wind drag, revealing its impact on dust dynamics and resonant structure contrast across stellar types.

Findings

Resonant ring structures form around all considered stellar types.

Stellar wind drag can dominate over Poynting-Robertson drag around old M-type stars.

Optical depth contrast of resonant rings increases for lower-mass stars.

Abstract

Earth-like exoplanets can create resonant structures in exozodiacal dust through mean motion resonances (MMRs). These structures not only suggest the presence of such planets, but also act as potential noise sources in future mid-infrared (MIR) nulling interferometry observations. We aim to investigate how resonant structures in exozodiacal dust vary across stellar spectral types (F4--M4), and to evaluate how stellar wind drag affects their morphology and brightness in mature planetary systems. We conducted numerical simulations of dust dynamics, extending earlier studies by including spectral type variation in stellar wind drag in addition to Poynting-Robertson (PR) drag. Our models represented systems of a few Gyr hosting an Earth-like exoplanet in the habitable zone (HZ). We produced spatially resolved maps of optical depth and thermal emission for different stellar spectral types. Our simulations showed that resonant ring structures were formed for all stellar spectral types considered. In particular, we found that stellar wind drag played a critical role in shaping dust dynamics around old M-type stars, where it could dominate over PR drag by a factor of approximately 44. This reduced the contrast of resonant rings relative to the background disk, compared to cases without spectral type variation in stellar wind. Across different spectral types, the optical depth contrast of the resonant ring increased for lower-mass stars, assuming a fixed background level. Asymmetric thermal emission distributions were derived across all spectral types, which peaked for K-type stars. Our findings highlight the importance of incorporating both resonant dynamics and stellar wind effects when modeling exozodiacal dust around stars of different spectral types.