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

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<SUP>+</SUP> (<inline-formula> </inline-formula>) in K-band. We carry out free atmospheric retrieval analyses to constrain chemical and isotopic abundances, temperature structures, rotation velocities (<inline-formula> </inline-formula>), and radial velocities. We confirm the previous detection of <SUP>13</SUP>CO in YSES 1 b at a higher significance of 12.6σ, but point to a higher <SUP>12</SUP>CO/<SUP>13</SUP>CO ratio of 88 ± 13 (1σ 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<SUB>2</SUB>O and CO in the outer planet YSES 1 c at 7.3σ and 5.7σ, 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 <inline-formula> </inline-formula>, 5.34 ± 0.14 km s<SUP>‑1</SUP> for YSES 1 b and 11.3 ± 2.1 km s<SUP>‑1 </SUP>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.