The Doppler Shadow of WASP-3b: A tomographic analysis of Rossiter-McLaughlin observations

摘要

Hot-Jupiter planets must form at large separations from their host starswhere the temperatures are cool enough for their cores to condense. They thenmigrate inwards to their current observed orbital separations. Differenttheories of how this migration occurs lead to varying distributions of orbitaleccentricity and the alignment between the rotation axis of the star and theorbital axis of the planet. The spin-orbit alignment of a transiting system isrevealed via the Rossiter-McLaughlin effect, which is the anomaly present inthe radial velocity measurements of the rotating star during transit due to theplanet blocking some of the starlight. In this paper we aim to measure thespin-orbit alignment of the WASP-3 system via a new way of analysing theRossiter-McLaughlin observations. We apply a new tomographic method foranalysing the time variable asymmetry of stellar line profiles caused by theRossiter-McLaughlin effect. This new method eliminates the systematic errorinherent in previous methods used to analyse the effect. We find a value forthe projected stellar spin rate of v sin i = 13.9 \pm 0.03 km/s which is inagreement with previous measurements but has a much higher precision. Thesystem is found to be well aligned which favours an evolutionary history forWASP-3b involving migration through tidal interactions with a protoplanetarydisc. Using gyrochronology we estimate the age of the star to be ~300 Myr withan upper limit of 2 Gyr from comparison with isochrones.