Spectra of AF Lep b using SPHERE & GRAVITY from VLT

Although the majority of exoplanets are expected to form via core accretion, most directly imaged exoplanets have not been convincingly demonstrated to follow this formation pathway. We obtained new interferometric observations of the directly imaged giant planet AF Lep b with the VLTI/GRAVITY instrument.

We present three epochs of ~50uas relative astrometry and the K-band spectrum of the planet for the first time at a resolution of R=500. Using only these measurements, spanning less than 2 months, and the Hipparcos-Gaia Catalogue of Accelerations, we are able to significantly constrain the planet's orbit; this bodes well for interferometric observations of planets discovered by Gaia DR4. Including all available measurements of the planet, we infer an effectively circular orbit (e<0.02, 0.07, and 0.13 at 1{sigma}, 2{sigma}, and 3{sigma}, respectively) in spin-orbit alignment with the host and measure a dynamical mass of Mp=3.75+/-0.5MJup.