New Orbital Constraints for YSES 1 b and HR 2562 B from High-Precision Astrometry and Planetary Radial Velocities^∗

Abstract We present new VLTI/GRAVITY astrometry and updated orbit fits for the directly imaged companions YSES 1 b and HR 2562 B, substellar objects straddling the planet–brown-dwarf boundary. Using high-precision astrometry, radial velocity data, and proper motions, we derive revised orbital parameters with orbitize! . For YSES 1 b, the inclusion of GRAVITY astrometry and a relative radial velocity measurement from Y. Zhang et al. (2024) overcomes the traditional challenge of constraining eccentricities for distant companions, enabling the first orbit fit and yielding a constrained eccentricity of 0.44 ± 0.20. This represents the first full orbit fit for the system. Additionally, we calculate a median line-of-sight stellar obliquity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>1</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>11</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> deg, providing further insight into the system’s dynamical architecture. For HR 2562 B, our analysis agrees with S. Y. Zhang et al., confirming a low-eccentricity orbit (0.34 ± 0.20) and an inclination of 87 ± 1 deg. We find HR 2562 B’s orbit to be nearly coplanar with the debris disk, with a mutual inclination of 3.7 ± 0.3 deg. For both YSES 1 b and HR 2562 B the lower eccentricities favor an in situ formation scenario over extreme scattering or cloud fragmentation.