Investigating exoplanet systems with the Rossiter-McLaughlin effect

Background:

Since the discovery of the first exoplanet around a sun-like star almost 3 decades ago, enormous progress has been made. The number of known exoplanets has increased to over 5000 today. Even more interestingly, we have started to probe the atmospheres of some these planets using telescopes in space and on the ground.

In most cases, these studies focus on transiting planets where we can either study the atmosphere in transmission as it passes between the Earth and the star, which allows a direct determination of the composition and extent of the atmosphere. In addition, when these planets transit, they block parts of the stellar surface rotating at different velocities. This causes an apparent shift in the radial velocity of the star from which it is possible to deduce the (mis)alignment between the stellar rotation axis and the axis of the planet’s orbit. This effect is known as the Rossiter-McLaughlin (RM) effect.

As the RM effect depends not only on the planet’s orbital properties and the stellar rotation, but also on the size of the planet, it is possible to use it as a way to characterise the broad-band transmission spectrum of a planet using the Chromatic RM effect.

This project:

The aim of this project is to take advantage of the chromatic RM effect to investigate the broadband transmission spectra of a wide range of exoplanets. Rather than measuring the apparent shift in velocities as the planet blocks different parts of the stellar surface, we will directly model the stellar line-profile to make a full fit to the available data and improve the detection limits. 

To obtain the high-precision line-profiles needed for this analysis, we will build on the ACID code (Dolan et al. 2024) developed at Queen’s University Belfast.

In addition, to characterising the planet’s atmosphere, we can also investigate the properties of starspots, when a planet crosses these spots and blocks part of their light. Finally, we can look for the presence of exorings and exomoons, as they will produce a very distinct distortion of the stellar line-profile.

For further information please contact Dr Ernst de Mooij (e.demooij@qub.ac.uk)