The shocking transit of WASP-12b: Modelling the observed early ingress in the near ultraviolet

TL;DR

This paper models the stellar wind environment of WASP-12b to explain the observed early ingress in near ultraviolet transits, supporting the hypothesis that a bow shock causes this phenomenon.

Contribution

It introduces a detailed plasma environment model and Monte Carlo simulations to reproduce the early ingress, advancing understanding of exoplanet magnetospheric interactions.

Findings

Reproduced early ingress with various plasma conditions.

Supported bow shock as explanation for UV transit features.

Demonstrated the impact of shock geometry and optical depth.

Abstract

Near ultraviolet observations of WASP-12b have revealed an early ingress compared to the optical transit lightcurve. This has been interpreted as due to the presence of a magnetospheric bow shock which forms when the relative velocity of the planetary and stellar material is supersonic. We aim to reproduce this observed early ingress by modelling the stellar wind (or coronal plasma) in order to derive the speed and density of the material at the planetary orbital radius. From this we determine the orientation of the shock and the density of compressed plasma behind it. With this model for the density structure surrounding the planet we perform Monte Carlo radiation transfer simulations of the near UV transits of WASP-12b with and without a bow shock. We find that we can reproduce the transit lightcurves with a wide range of plasma temperatures, shock geometries and optical depths. Our results support the hypothesis that a bow shock could explain the observed early ingress.