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 3.2−0.6+0.7MJup, semi-major axis of 8.4−1.3+1.1 au, and eccentricity of 0.24−0.15+0.27. 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∗=54−9+11∘) and orbital inclination (io=50−12+9∘) 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.
@article{arxiv.2302.05420,
title = {Astrometric Accelerations as Dynamical Beacons: A Giant Planet Imaged Inside the Debris Disk of the Young Star AF Lep},
author = {Kyle Franson and Brendan P. Bowler and Yifan Zhou and Tim D. Pearce and Daniella C. Bardalez Gagliuffi and Lauren Biddle and Timothy D. Brandt and Justin R. Crepp and Trent J. Dupuy and Jacqueline Faherty and Rebecca Jensen-Clem and Marvin Morgan and Aniket Sanghi and Christopher A. Theissen and Quang H. Tran and Trevor A. Wolf},
journal= {arXiv preprint arXiv:2302.05420},
year = {2023}
}