A new atmospheric characterization of the sub-stellar companion HR 2562 B with JWST/MIRI observations

Context. HR 2562 B is a planetary-mass companion at an angular separation of 0.56″ (19 au) from the host star, which is also a member of a select number of L/T transitional objects orbiting a young star. This companion gives us a great opportunity to contextualize and understand the evolution of young objects in the L/T transition. However, the main physical properties (e.g., T eff and mass) of this companion have not been well constrained (34% uncertainties on T eff , 22% uncertainty for log( g )) using only near-infrared (NIR) observations. Aims. We aim to narrow down some of its physical parameters uncertainties (e.g., T eff : 1200–1700 K, log( g ): 4–5) incorporating new observations in the Rayleigh-Jeans tail with the JWST/MIRI filters at 10.65, 11.40, and 15.50 μm, as well as to understand its context in terms of the L/T transition and chemical composition. Methods. We processed the MIRI observations with reference star differential imaging (RDI) and detect the companion at high S/N (around 16) in the three filters, allowing us to measure its flux and astrometry. We used two atmospheric models, ATMO and Exo-REM , to fit the spectral energy distribution using different combinations of mid-IR and near-IR datasets. We also studied the color-magnitude diagram using the F1065C and F1140C filters combined with field brown dwarfs to investigate the chemical composition in the atmosphere of HR 2562 B, as well as a qualitative comparison with the younger L/T transitional companion VHS 1256 b. Results. We improved the precision on the temperature of HR 2562 B ( T eff = 1255 K) by a factor of 6× compared to previous estimates (±15 K vs ±100 K) using ATMO . The precision of its luminosity was also narrowed down to −4.69 ± 0.01 dex. The surface gravity still presents a wider range of values (4.4 to 4.8 dex). While its mass was not narrowed down, we find the most probable values between 8 M Jup (3− σ lower limit from our atmospheric modeling) and 18.5 M Jup (from the upper limit provided by astrometric studies). We report a sensitivity to objects of mass ranging between 2–5 M Jup at 100 au, reaching the lower limit at F1550C . We also implemented a few improvements in the pipeline related to the background subtraction and stages 1 and 2. Conclusions. HR 2562 B has a mostly (or near) cloud-free atmosphere, with the ATMO model demonstrating a better fit to the observations. From the color-magnitude diagram, the most probable chemical species at MIR wavelengths are s