Direct imaging discovery of a super-Jovian around the young Sun-like star AF Leporis

Abstract

Context. Expanding the sample of directly imaged companions to nearby, young stars that are amenable to detailed astrometric and spectroscopic studies is critical for the continued development and validation of theories of their evolution and atmospheric processes. Aims. The recent release of the Gaia astrometric catalog allows us to efficiently search for these elusive companions by targeting those stars that exhibit the astrometric reflex motion induced by an orbiting companion. The nearby (27 pc), young (24 Myr) star AF Leporis (AF Lep) was targeted because of its significant astrometric acceleration measured between the HIPPARCOS and Gaia astrometric catalogs, consistent with a wide-orbit planetary-mass companion detectable with high-contrast imaging. Methods. We used the SPHERE instrument on the VLT to search for faint substellar companions in the immediate vicinity of AF Lep. We used observations of a nearby star interleaved with those of AF Lep to efficiently subtract the residual point spread function. This provided sensitivity to faint planetary-mass companions within 1″ (~30 au) of the star. Results. We detected the companion AF Lep b at a separation of 339 mas (9 au) from the host star, at almost the exact location predicted by the astrometric acceleration, and within the inner edge of its unresolved debris disk. The measured K-band contrast and the age of the star yield a model-dependent mass of between 4 and 6 MJup, consistent with the mass derived from an orbital fit to the absolute and relative astrometry of 4.3−1.2+2.9 MJup. The near-infrared spectral energy distribution of the planet is consistent with an object at the L−T spectral type transition, but under-luminous with respect to field-gravity objects. Conclusions. AF Lep b joins a growing number of substellar companions imaged around stars in the young β Pictoris moving group. With a mass of between 3 and 7 MJup, it occupies a gap in this isochronal sequence between hotter, more massive companions, such as PZ Tel B and β Pic b, and the cooler 51 Eri b, which is sufficiently cool for methane to form within its photosphere. Lying at the transition between these two classes of objects, AF Lep b will undoubtedly become a benchmark for studies of atmospheric composition and processes, as well as an anchor for models of the formation and evolution of substellar and planetary-mass companions.

AF Lep b: The lowest-mass planet detected by coupling astrometric and direct imaging data

“…An independent and contemporaneous discovery of this companion is presented in De Rosa et al (2023) and in Franson et al (2023b).…”

Vortex fiber nulling for exoplanet observations: implementation and first light

“…By combining Hipparcos 18 , 19 and Gaia 20 , 21 astrometry to identify and target accelerating stars that show promise for harboring a substellar companion, 22 – 24 the yield of recent direct imaging surveys has been improved 25 – 29 Nevertheless, these campaigns use coronagraphs, which are limited to separations ≳3 λ/D from the star (∼13 AU at 100 parsec for λ=2.2 μm and D=10 m), where λ is the wavelength and D is the telescope diameter. RV surveys 30 , 31 suggest that the peak in the giant planet population is closer to the star than state-of-the-art AO imaging survey instruments can currently access, 32 , 33 indicating that the yield can be further improved by unlocking access to these smaller separations.…”

Dynamical Mass of the Young Brown Dwarf Companion PZ Tel B

“…The sample of substellar companions with dynamical masses and age constraints now amounts to ≈20 brown dwarf companions (e.g., Cheetham et al 2018;Brandt et al 2019Brandt et al , 2020Brandt et al , 2021cBonavita et al 2022;Franson et al 2022;Kuzuhara et al 2022;Franson et al 2023a;Li et al 2023) and giant planets (Dupuy et al 2019;Lagrange et al 2019;Nowak et al 2020;Brandt et al 2021a;Hinkley et al 2022;Franson et al 2023b;De Rosa et al 2023;Mesa et al 2023). Most of these benchmark companions orbit old field stars (>1 Gyr); only three planets-β Pic b, β Pic c, and AF Lep b-are young (<200 Myr) and have precise ages based on membership in kinematic associations (Dupuy et al 2019;Nowak et al 2020;Brandt et al 2021a;Franson et al 2023b;De Rosa et al 2023;Mesa et al 2023). 2 Age-dating individual field stars is notoriously challenging, which can limit the precision of model tests for benchmark companions around young field stars (see e.g., HD 984 B; Franson et al 2022) compared to objects in young moving groups.…”