Astrometric Accelerations as Dynamical Beacons: A Giant Planet Imaged inside the Debris Disk of the Young Star AF Lep

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 ind...

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Bibliographic Details
Published in:Astrophysical journal. Letters 2023-06, Vol.950 (2), p.L19
Main Authors: Franson, Kyle, Bowler, Brendan P., Zhou, Yifan, Pearce, Tim D., Bardalez Gagliuffi, Daniella C., Biddle, Lauren I., Brandt, Timothy D., Crepp, Justin R., Dupuy, Trent J., Faherty, Jacqueline, Jensen-Clem, Rebecca, Morgan, Marvin, Sanghi, Aniket, Theissen, Christopher A., Tran, Quang H., Wolf, Trevor N.
Format: Article
Language:English
Subjects:
Astrometric exoplanet detection
Coronagraphs
Debris
Debris disks
Direct imaging
Extrasolar gaseous giant planets
Inclination
Orbit determination
Planets
Stars
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Summary: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 + 0.7 M Jup , semimajor 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 ( i o = 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.
ISSN:2041-8205
2041-8213
DOI:10.3847/2041-8213/acd6f6