Article Summary #5

The spin-orbit angle of the transiting hot Jupiter CoRoT-1b

Pont, F.; Endl, M.; Cochran, W. D.; Barnes, S. I., et al. , 2010, Volume 402, Issue 1, Pages L1-L5
http://www3.interscience.wiley.com/cgi-bin/fulltext/123208852/HTMLSTART?CRETRY=1&SRETRY=0

This paper presents an extremely interesting result of a measurement of the angle between the orbit of the planet CoRoT-1b and the normal to the rotational axis of its host star.

The Rossier-McKaughlin effect is used to measure the angle between the rotation axis of a star and the orbit plane of one of its orbiting planets. This method involves analyzing the changes in the radial velocity of the star when the planet passes in from of it (this is also called transiting). The observations and analysis of the distribution of these planetary spin-orbit angles are very important for gaining a deeper understanding of the evolution of stellar systems in general.

CoRoT-1b is a hot-Jupiter type of exoplanet, with a very short orbital period of 1.5 days. This quick orbit implies that the massive planet (with approximately the same mass as Jupiter) is very close to its host star from which it absorbs radiation and its temperature increases, thus the name “hot Jupiter”.

For this analysis, the measurements were made with high-accuracy photometry from a camera on the European Southern Observatory in Chile, and with radial velocity spectroscopic data from the spectrographs SOPHIE (Spectrographe pour l’Observation des Phénomènes des Intérieurs stellaires et des Exoplanètes) and HARPS (High Accuracy Radial velocity Planet Searcher). Pont et al. 2010 got the physical parameters of the transit from standard spectroscopic measurements.

The results were unexpected: they found a spin-orbit angle of 77̊, almost perpendicular (in comparison with the inclination of the Earth relative to the sun which is almost zero). They argue that the most probable explanation would be that the hot Jupiter ended up in such an unusual position due to being hit by another object of comparable size.