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 + ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi class="MJX-tex-calligraphic" mathvariant="script">R</mml:mi> </mml:mrow> <mml:mspace width="0.25em"/> <mml:mo>∼</mml:mo> <mml:mspace width="0.25em"/> <mml:mtext>100,000</mml:mtext> </mml:math> ) in K -band. We carry out free atmospheric retrieval analyses to constrain chemical and isotopic abundances, temperature structures, rotation velocities ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>v</mml:mi> <mml:mi>sin</mml:mi> <mml:mi>i</mml:mi> </mml:math> ), 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>v</mml:mi> <mml:mi>sin</mml:mi> <mml:mi>i</mml:mi> </mml:math> , 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.