Orbital obliquities of transiting planets from starspot occultations

TL;DR

This paper presents a method to measure the orbital obliquities of transiting exoplanets by analyzing starspot occultations during transits, providing insights into star-planet alignment especially for cool stars.

Contribution

It introduces a novel technique to determine true and sky-projected orbital obliquities using starspot crossing events, complementing existing methods like the Rossiter-McLaughlin effect.

Findings

Compiled a catalogue of lambda and psi measurements from starspot crossings.

Demonstrated the method's effectiveness for cool stars with transiting planets.

Provided initial results and analysis for multiple star-planet systems.

Abstract

When a planet passes in front of a starspot during a transit of its host star, it causes a small upward blip in the light curve. Modelling the transit with the starspot allows the size, brightness and position of the spot to be measured. If the same spot can be observed in two different transits, it is possible to track the motion of the spot due to the rotation of the star. The rotation period and velocity of the star (Prot and Vsini) and the sky-projected orbital obliquity of the system (lambda) can then be determined. If one has three or more observations of the same spot, the true orbital obliquity (psi) can be measured. We are performing this analysis for a number of cool stars orbited by transiting planets. We present our results so far and compile a catalogue of lambda and psi measurements from spot crossing events. The method is particularly useful for cool stars, and is therefore complementary to studies of the Rossiter-McLaughlin effect, which perform better on hotter and faster-rotating stars.