PSO J318.5−22: an 8 Jupiter Mass Free Floating (?) Exoplanet Confirmed to be Part of the β Pictoris Moving Group

The Radial and Rotational Velocities of PSO J318.5338−22.8603, a Newly Confirmed Planetary-Mass Member of the β Pictoris Moving Group

Authors:

Allers et al

Abstract:

PSO J318.5338−22.8603 is an extremely-red planetary-mass object that has been identified as a candidate member of the β Pictoris moving group based on its spatial position and tangential velocity. We present a high resolution K-band spectrum of PSO J318.5338−22.8603. Using a forward-modeling Markov Chain Monte Carlo approach, we report the first measurement of the radial velocity and v sin(i) of PSO J318.5−22, −6.0+0.8−1.1 km s−1 and 17.5+2.3−2.8 km s−1, respectively. We calculate the space velocity and position of PSO J318.5−22 and confirm that it is a member of the β Pictoris moving group. Adopting an age of 23±3 Myr for PSO J318.5−22, we determine a mass of 8.3±0.5 MJup and effective temperature of 1127+24−26 K using evolutionary models. PSO J318.5338−22.8603 is intermediate in mass and temperature to the directly-imaged planets β Pictoris b and 51 Eridani b, making it an important benchmark object in the sequence of planetary-mass members of the β Pictoris moving group. Combining our v sin(i) measurement with recent photometric variability data, we constrain the inclination of PSO J318.5−22 to greater than 29∘ and its rotational period to 5-10.2 hours. The equatorial velocity of PSO J318.5−22 indicates that its rotation is consistent with an extrapolation of the velocity-mass relationship for solar system planets.