The JWST weather report from the nearest brown dwarfs III: Heterogeneous clouds and Thermochemical instabilities as possible drivers of WISE 1049AB's spectroscopic variability

TL;DR

This study analyzes JWST spectroscopic data of the brown dwarf binary WISE 1049AB, revealing wavelength-dependent variability likely driven by thermochemical instabilities and complex cloud interactions, advancing understanding of substellar atmospheres.

Contribution

It provides the first detailed 3D atmospheric mapping of WISE 1049AB using molecular band variability, highlighting thermochemical instabilities as key drivers of spectroscopic variability.

Findings

Higher variability in CO and CH4 bands compared to H2O.

Clouds alone cannot explain the observed variability patterns.

Thermochemical instabilities likely influence atmospheric dynamics.

Abstract

We present a new analysis of the spectroscopic variability of WISE~J104915.57$-$531906.1AB (WISE~1049AB, L7.5+T0.5), observed using the NIRSpec instrument onboard the James Webb Space Telescope (GO 2965 - PI: Biller). We explored the variability of the dominant molecular bands present in their 0.6--5.3~$\mu$m spectra (H$_2$O, CH$_4$, CO), finding that the B component exhibits a higher maximum deviation than the A component in all the wavelength ranges tested. The light curves reveal wavelength-(atmospheric depth) and possibly chemistry-dependent variability. In particular, for the A component, the variability in the light curves at the wavelengths traced by the CH$_4$ and CO molecular absorption features is higher than that of H$_2$O, even when both trace similar pressure levels. We concluded that clouds alone are unlikely to explain the increased variability of CO and CH$_4$ with respect to H$_2$O, suggesting that an additional physical mechanism is needed to explain the observed variability. This mechanism is probably due to thermochemical instabilities. Finally, we provide a visual representation of the 3D atmospheric map reconstructed for both components using the molecular band contributions at different pressure levels and the fit of planetary-scale waves.