The ESO SupJup Survey. III. Confirmation of 13CO in YSES 1 b and Atmospheric Detection of YSES 1 c with CRIRES+

Abstract

High-resolution spectroscopic characterization of young super-Jovian planets enables precise constraints on elemental and isotopic abundances of their atmospheres. As part of the ESO SupJup Survey, we present high-resolution spectral observations of two wide-orbit super-Jupiters in YSES 1 (or TYC 8998-760-1) using the upgraded VLT/CRIRES ^+ ( ${ \mathcal R }\,\sim \,\rm{100,000}$ ) in K -band. We carry out free atmospheric retrieval analyses to constrain chemical and isotopic abundances, temperature structures, rotation velocities ( $v\sin i$ ), and radial velocities. We confirm the previous detection of ^13 CO in YSES 1 b at a higher significance of 12.6 σ , but point to a higher ^12 CO/ ^13 CO ratio of 88 ± 13 (1 σ confidence interval), consistent with the primary’s isotope ratio 66 ± 5. We retrieve a solar-like composition in YSES 1 b with a C/O = 0.57 ± 0.01, indicating a formation via gravitational instability or core accretion beyond the CO iceline. Additionally, the observations lead to detections of H _2 O and CO in the outer planet YSES 1 c at 7.3 σ and 5.7 σ , respectively. We constrain the atmospheric C/O ratio of YSES 1 c to be either solar or subsolar (C/O = 0.36 ± 0.15), indicating the accretion of oxygen-rich solids. The two companions have distinct $v\sin i$ , 5.34 ± 0.14 km s ^−1 for YSES 1 b and 11.3 ± 2.1 km s ^−1 for YSES 1 c, despite their similar natal environments. This may indicate different spin axis inclinations or effective magnetic braking by the long-lived circumplanetary disk around YSES 1 b. YSES 1 represents an intriguing system for comparative studies of super-Jovian companions and linking present atmospheres to formation histories.

Keywords

• Exoplanet atmospheres
• High resolution spectroscopy
• Substellar companion stars