# The Rossiter-McLaughlin effect of CoRoT-3b & HD189733b

## TL;DR

This study measures the spin-orbit alignment of exoplanets HD 189733b and CoRoT-3b using the Rossiter-McLaughlin effect, revealing a near-aligned orbit for HD 189733b and a tentative misalignment for CoRoT-3b, with implications for planetary system formation.

## Contribution

First precise measurement of the spin-orbit angle for HD 189733b using combined spectroscopic and photometric data, and analysis of CoRoT-3b's potential misalignment.

## Key findings

- HD 189733b has a near-zero spin-orbit angle (beta ≈ 0.85°).
- CoRoT-3b shows a possible non-zero inclination (beta ≈ 37.6°), but with large uncertainties.
- Systematic effects impact the accuracy of stellar rotation velocity measurements.

## Abstract

We present radial-velocity sequences acquired during three transits of the exoplanet HD 189733b and one transit of the CoRoT-3b. We applied a combined Markov-Chain Monte Carlo analysis of spectroscopic and photometric data on these stars, to determine a full set of system parameters including the project spin-orbit misalignement angle of HD 189733b to an unprecedented precision via the Rossiter-McLaughlin effect: beta = 0.85 degrees (+0.32 -0.28) . This small but non-zero inclination of the planetary orbit is important to understand the origin of the system. On CoRoT-3b, results seem to point towards a non-zero inclination as well with beta = 37.6 degrees (+10.0 -22.3), but this remains marginal. Systematic effects due to non-gaussian cross-correlation functions appear to be the main cause of significant residuals that prevent an accurate determination of the projected stellar rotation velocity V sin(I) for both stars.