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Arxiv: A new atmospheric characterization of the sub-stellar companion HR\,2562\,B with JWST/MIRI observations Published: 9/6/2024 9:00:03 PM Updated: 9/6/2024 9:00:03 PM

Paper abstract: Context: HR2562B is a planetary-mass companion located 0.56arcsec (19au) fromits host star. It is one of a few L/T transitional objects orbiting a youngstar. This companion provides insight into the evolution of young objects inthe L/T transition. However, its key physical properties, such as Teff andmass, remain poorly constrained, with large uncertainties (34% for Teff, 22%for log(g)) based on near-infrared observations alone. Aims: We aim to refinethese uncertainties, especially for Teff (1200-1700K) and log(g) (4-5), usingnew MIR data from the JWST/MIRI filters (10.65, 11.40, and 15.50 microns), andbetter understand the companion's chemical composition and its role in the L/Ttransition. Methods: MIRI data were processed using reference star differentialimaging, revealing HR2562B at high S/N (16) in all 3 filters. We used 2atmospheric models, ATMO and ExoREM, to fit the SED, combining MIR and NIRdatasets. Additionally, we used CMD with brown dwarfs to explore the chemicalcomposition of HR2562B's atmosphere and compare it to another L/T transitionobject, VHS1256b. Results: Our analysis improved the temperature precision(Teff=1255+-15K) by 6x compared to previous estimates. We also narrowed itsluminosity to -4.69+-0.01 dex. Surface gravity remains uncertain (4.4-4.8), andits mass is estimated between 8 and 18.5Mj, depending on modeling andastrometry. Sensitivity analysis revealed the ability to detect objects between2-5Mj at 100au. Conclusions: HR2562B likely has a near cloud-free atmosphere,with the ATMO model fitting better than ExoREM. Silicate absorption featuresare weak, requiring further spectroscopic observations. While HR2562B andVHS1256b share similarities, they are in different evolutionary stages, makingHR2562B key to understanding young objects in the L/T transition. It is likelya planetary-mass companion, suggesting a reclassification as HR2562b.