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

**Authors:** Kyle Franson, Brendan P. Bowler, Yifan Zhou, Tim D. Pearce, Daniella C. Bardalez Gagliuffi, Lauren Biddle, Timothy D. Brandt, Justin R. Crepp, Trent J. Dupuy, Jacqueline Faherty, Rebecca Jensen-Clem, Marvin Morgan, Aniket Sanghi, Christopher A. Theissen, Quang H. Tran, Trevor A. Wolf  
**arXiv:** [2302.05420](https://arxiv.org/abs/2302.05420)  
**Date:** 2023-02-10  
**Summary page:** https://www.summarizepaper.com/en/paper/2302.05420v1/

## Key points

- A giant planet named AF Lep b has been discovered orbiting the young star AF Lep
- The planet was detected through high-contrast imaging using Keck/NIRC2 observations in $L'$ with the Vector Vortex Coronagraph
- AF Lep b exhibits orbital motion at the 6-$\sigma$ level over the course of 13 months
- The planet's dynamical mass is 3.2$^{+0.7}_{-0.6}$ $M_\mathrm{Jup}$, semi-major axis is $8.4^{+1.1}_{-1.3}$ au, and eccentricity is $0.24^{+0.27}_{-0.15}$
- AF Lep b is the lowest-mass imaged exoplanet with a dynamical mass measurement to date
- The host star also hosts a debris disk located at $\sim$50 au, but it is unlikely to be sculpted by AF Lep b, suggesting there may be additional planets in this system at wider separations yet to be discovered
- Both stellar inclination ($i_* = 54^{+11}_{-9} {}^\circ$) and orbital inclination ($i_o = 50^{+9}_{-12} {}^\circ$) are in good agreement with each other - an observation consistent with spin-orbit alignment - furthering our understanding of exoplanetary systems around young stars like AF Lep b's host star
- This research was conducted as part of an ongoing program targeting stars with astrometric accelerations between Hipparcos and Gaia that indicate the presence of substellar companions; thus far yielding promising results that have been submitted to ApJL for publication

## Summary

A team of astronomers has discovered a giant planet orbiting the young star AF Lep, which is a member of the 24 $\pm$ 3 Myr $\beta$ Pic moving group. The planet was detected through high-contrast imaging using Keck/NIRC2 observations in $L'$ with the Vector Vortex Coronagraph. The point source, named AF Lep b, exhibits orbital motion at the 6-$\sigma$ level over the course of 13 months. A joint orbit fit yields precise constraints on the planet's dynamical mass of 3.2$^{+0.7}_{-0.6}$ $M_\mathrm{Jup}$, semi-major axis of $8.4^{+1.1}_{-1.3}$ au, and eccentricity of $0.24^{+0.27}_{-0.15}$. This makes AF Lep b the lowest-mass imaged exoplanet with a dynamical mass measurement to date and highlights its promise as a tool for finding and characterizing long-period planets and providing insight into planetary formation theories for young stars like AF Lep. The host star also hosts a debris disk located at $\sim$50 au; however, it is unlikely to be sculpted by AF Lep b, suggesting there may be additional planets in this system at wider separations yet to be discovered. Furthermore, both stellar inclination ($i_* = 54^{+11}_{-9} {}^\circ$) and orbital inclination ($i_o = 50^{+9}_{-12} {}^\circ$) are in good agreement with each other - an observation consistent with spin-orbit alignment - furthering our understanding of exoplanetary systems around young stars like AF Lep b's host star. This research was conducted as part of an ongoing program targeting stars with astrometric accelerations between Hipparcos and Gaia that indicate the presence of substellar companions; thus far yielding promising results that have been submitted to ApJL for publication and will hopefully continue to expand our knowledge about exoplanets in our universe through this method going forward.