Volume 567, July 2014
|Number of page(s)||8|
|Section||Planets and planetary systems|
|Published online||08 July 2014|
Spin-orbit angle distribution and the origin of (mis)aligned hot Jupiters
Laboratoire Lagrange, UMR 7293, Université Nice
Sophia-antipolis/CNRS/Observatoire de la Côte d’Azur,
2 Institute for Theory and Computation, Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge MA 02138, USA
Accepted: 7 April 2014
Context. For 61 transiting hot Jupiters, the projection of the angle between the orbital plane and the stellar equator (called the spin-orbit angle) has been measured. For about half of them, a significant misalignment is detected, and retrograde planets have been observed. This challenges scenarios of the formation of hot Jupiters.
Aims. In order to better constrain formation models, we relate the distribution of the real spin-orbit angle Ψ to the projected one β. Then, a comparison with the observations is relevant.
Methods. We analyse the geometry of the problem to link analytically the projected angle β to the real spin-orbit angle Ψ. The distribution of Ψ expected in various models is taken from the literature, or derived with a simplified model and Monte Carlo simulations in the case of the disk-torquing mechanism.
Results. An easy formula to compute the probability density function (PDF) of β knowing the PDF of Ψ is provided. All models tested here look compatible with the observed distribution beyond 40 degrees, which is so far poorly constrained by only 18 observations. But only the disk-torquing mechanism can account for the excess of aligned hot Jupiters, provided that the torquing is not always efficient. This is the case if the exciting binaries have semi-major axes as large as ~104 AU.
Conclusions. Based on comparison with the set of observations available today, scattering models and the Kozai cycle with tidal friction models can not be solely responsible for the production of all hot Jupiters. Conversely, the presently observed distribution of the spin-orbit angles is compatible with most hot Jupiters having been transported by smooth migration inside a proto-planetary disk, itself possibly torqued by a companion.
Key words: planets and satellites: formation / planets and satellites: dynamical evolution and stability / planet-disk interactions / methods: statistical
© ESO, 2014
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.