kappa And JWST/MIRI images

We obtained JWST/MIRI coronagraphic data in the F1065C, F1140C, and F1550C filters and recalibrated existing NIR photometry using an updated ATLAS stellar model. We used MIRI color-magnitude diagrams to probe the likelihood of species (e.g., CH_4_, NH_3_, and silicates). We compared the H and F1140C colors and magnitudes of the companion to isochrones to constrain the age and mass.

We then modeled its spectral energy distribution with atmospheric models to refine the estimates of Teff, radius, and log(g) and to constrain age and mass using evolutionary models. Cloudy atmosphere models fit the spectral energy distribution of kappa And b best. This is consistent with its L0/L2 spectral type and its position near silicate- atmosphere field objects in the MIRI color-magnitude diagram.

We derived an age of 47+/-7Myr and a mass of 17.3+/-1.8MJup by weight-mean combining the models. Atmospheric modeling yielded Teff=1791+/-68K and a radius of 1.42+/-0.06RJup . This improves the precision by ~ 30% over previous estimates.

Log(g) was constrained to 4.35+/-0.07dex, which is an improvement in the precision by ~70% relative to the most precise literature value of 4.75+/-0.25 dex. Our new mass estimate places kappa And b slightly above the planet-brown dwarf boundary determined by the deuterium-burning limit. Our age estimate is ~75% more precise than previous values and aligns the object with the Columba association (42Myr).

The derived Teff suggests silicate clouds, but this needs to be confirmed spectroscopically. MIRI data were crucial to refine the radius and temperature, which led to stronger constraints on the age and mass (both dependent on the model) and improved the overall characterization of kappa And b.