Direct imaging discovery of a young giant planet orbiting on Solar System scales

TL;DR

This paper reports the direct imaging discovery of a young giant planet, HD 135344 Ab, orbiting close to its star at about 15-20 au, providing insights into early planetary formation and atmospheres.

Contribution

First direct imaging detection of a young giant planet on Solar System scales around HD 135344 A, confirmed with multi-epoch astrometry and spectroscopy.

Findings

Discovered a ~10 Mj planet at 15-20 au from HD 135344 A.

Confirmed the bound nature of the companion through astrometry.

Characterized the planet's atmosphere as young and planetary in nature.

Abstract

HD 135344 AB is a young visual binary system that is best known for the protoplanetary disk around the secondary star. The circumstellar environment of the A0-type primary star, on the other hand, is already depleted. HD 135344 A is therefore an ideal target for the exploration of recently formed giant planets because it is not obscured by dust. We searched for and characterized substellar companions to HD 135344 A down to separations of about 10 au. We observed HD 135344 A with VLT/SPHERE in the $H23$ and $K12$ bands and obtained $YJ$ and $YJH$ spectroscopy. In addition, we carried out VLTI/GRAVITY observations for the further astrometric and spectroscopic confirmation of a detected companion. We discovered a close-in young giant planet, HD 135344 Ab, with a mass of about 10 $M_\mathrm{J}$. The multi-epoch astrometry confirms the bound nature based on common parallax and common proper motion. This firmly rules out the scenario of a non-stationary background star. The semi-major axis of the planetary orbit is approximately 15-20 au, and the photometry is consistent with that of a mid L-type object. The inferred atmospheric and bulk parameters further confirm the young and planetary nature of the companion. HD 135344 Ab is one of the youngest directly imaged planets that has fully formed and orbits on Solar System scales. It is a valuable target for studying the early evolution and atmosphere of a giant planet that could have formed in the vicinity of the snowline.