SAC Seminar - Davide Gandolfi: Discerning exoplanet migration scenarios using the spin-orbit obliquity. Are hot Jupiters orbiting relatively hot stars preferentially misaligned ?
Oplysninger om arrangementet
Davide Gandolfi, Research and Scientific Support Department (RSSD) - European Space Agency - European Space Research and Technology Centre (ESA/ESTEC)
Gas giant planets orbiting within a few tenth of AU from their parent stars (hot Jupiters) are unlikely to have formed in situ and are clear evidence for planetary migration. Time-series spectroscopic observations of planetary transits allow us to measure the sky-projected system obliquity, i.e., the angle in the plane of the sky between the projections of the planet’s orbital angular momentum and the star’s rotation axis. As migration mechanisms differ in the degree to which they affect the orbit obliquity, measuring the spin-orbit obliquity of hot Jupiters provides us precious insights into planetary migration.
It has been empirically found that planets transiting stars hotter than 6250 K tend to be misaligned, suggesting that gravitational scattering by another body might be the dominant channel for producing hot Jupiters. However, the current sample of exoplanets orbiting relatively hot stars with secure measurements of the spin-orbit obliquity is not statistically significant yet to confirm this trend.
In this talk, I will present the first results of my pilot project to measure spectroscopically the spin-orbit obliquity of these poorly studied systems. By detecting the planetary Doppler shadow in the composite spectral line profile of the star, we measured the obliquity of three hot Jupiters transiting relatively hot stars and found that the systems are well aligned in the plane of the sky. An analysis of the tidal evolution of the systems shows how the currently measured obliquity and its uncertainty translate into an initial absolute value of less than a dozen degrees on the zero-age main sequence. Given the effective temperature of the stars (Teff>6250 K), these systems can be considered interesting exceptions to the above mentioned trend. Our findings are indicative of a smooth inward migration scenario that would not have perturbed the primordial low obliquity of the systems, involving angular momentum exchanges with the protoplanetary disc rather than gravitational scattering.