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Arxiv: The Retrieved Atmospheric Properties of the Sub-stellar Object VHS 1256 b from Analyzing HST, VLT and JWST Spectra Published: 9/12/2024 8:50:56 PM Updated: 9/12/2024 8:50:56 PM

Paper abstract: Motivated by the observed ~30% variations in flux from the L7 dwarf VHS 1256b, we subjected its time-resolved Hubble Space Telescope (HST) WFC3 spectra(measured in two epochs in 2018 and 2020), as well as medium-resolution VeryLarge Telescope (VLT) X-shooter and Early Release Science James Webb SpaceTelescope (JWST) spectra to a suite of both standard Bayesian (nested sampling)and machine-learning (random forest) retrievals. We find that both HST and VLTdata require vertically varying abundance profiles of water in order to modelthe spectra accurately. Despite the large flux variations observed in the HSTdata, the temporal variability cannot be attributed to a single varyingatmospheric property. The retrieved atmospheric quantities are consistent withbeing invariant across time. However, we find that model grids providegenerally poor fits to the measured HST spectra and are unsuitable forquantifying the temporal variability of atmospheric properties. Additionally,our analysis of JWST spectra using model grids indicates consistency inretrieved properties across different wavelength channels. Despite the temporalvariability in flux, the retrieved properties between HST and VLT, as well asbetween HST and JWST, are consistent within the respective posterioruncertainties. Such an outcome bodes well for future retrieval analyses ofexoplanetary atmospheres, which are expected to exhibit weaker flux variations.