An Imaged Giant Planet at AF Lep

Astrometric Accelerations as Dynamical Beacons: A Giant Planet Imaged Inside the Debris Disk of the Young Star AF Lep
https://arxiv.org/abs/2302.05420

Quote :

We present the direct imaging discovery of a giant planet orbiting the young star AF Lep, a 1.2 M⊙ member of the 24 ± 3 Myr β Pic moving group. AF Lep was observed as part of our ongoing high-contrast imaging program targeting stars with astrometric accelerations between Hipparcos and Gaia that indicate the presence of substellar companions. Keck/NIRC2 observations in L′ with the Vector Vortex Coronagraph reveal a point source, AF Lep b, at ≈340 mas which exhibits orbital motion at the 6-σ level over the course of 13 months. A joint orbit fit yields precise constraints on the planet's dynamical mass of 3.2+0.7−0.6 MJup, semi-major axis of 8.4+1.1−1.3 au, and eccentricity of 0.24+0.27−0.15. AF Lep hosts a debris disk located at ∼50 au, but it is unlikely to be sculpted by AF Lep b, implying there may be additional planets in the system at wider separations. The stellar inclination (i∗=54+11−9∘) and orbital inclination (io=50+9−12∘) are in good agreement, which is consistent with the system having spin-orbit alignment. AF Lep b is the lowest-mass imaged planet with a dynamical mass measurement and highlights the promise of using astrometric accelerations as a tool to find and characterize long-period planets.