Time-resolved JWST Retrieval Analysis of the Coldest Brown Dwarf: Temperature and Chemical Variations in WISE 0855-07
Abstract
WISE J0855-07 is the coldest known brown dwarf (estimated Teff~250 K), offering a rare opportunity to probe atmospheric physics in the temperature and mass regime that overlaps directly with exoplanets. At these temperatures, modest perturbations to the thermal structure and chemical abundances can produce measurable changes in the emergent mid-infrared spectrum, making time-resolved spectroscopy a powerful way to test whether the atmosphere is longitudinally and temporally homogeneous. Using James Webb Space Telescope NIRSpec/G395M time-series spectra spanning ~3 to 5.2 μm over 11 hr, we analyze every third spectrum from the dataset with a series of time-resolved atmospheric retrievals using the Brewster retrieval framework. Using this approach, we model epoch-to-epoch changes in the atmospheric state that drive the observed variability, including the thermal structure and key molecular abundances. From the time-series retrievals, we find that the primary source of the observed spectral variability is driven by the variations in the thermal structure, which range from ~1 to <100 K from epoch to epoch, particularly between the pressures of ~0.4 and 10 bar. In addition, changes in the abundances of CO, and possibly PH3 and CO2, further modulate the spectrum within specific molecular features. These measurements provide a retrieval-based view of atmospheric variability in an ultracold, planet-like object, directly constraining how thermal and chemical structure evolve on observable timescales.
Versions
Related
- Water Cloud and Chemical Modulations in the Coldest Brown Dwarf
- A Systematic Assessment of Total Stellar Mass Measurements with Spatially Resolved Photometry and Medium Bands at 1 < z < 9: The Impact of Mass-to-Light Variations and Outshining
- Chemical structure analysis of cosmic organic dust analogue using high-temperature vacuum Temperature-Programmed Desorption (TPD)
- Temperature-resolved sensitivities of 56Ni production to helium-burning reactions in pair-instability supernovae
- An Empirical Temperature Relation for Chemical Abundances in AGN
BibTeX
@misc{kothari2026timeresolved,
title = {{Time-resolved JWST Retrieval Analysis of the Coldest Brown Dwarf: Temperature and Chemical Variations in WISE 0855-07}},
author = {Harshil Kothari and Caroline V. Morley and Brittany E. Miles and Melanie J. Rowland and Natasha Batalha and Michael C. Cushing and Andrew J. Skemer and James Mang and Brianna Lacy and Johanna M. Vos and Channon Visscher and Adam C. Schneider and Genaro Suarez and Mikayla J. Wilson and Allison M. McCarthy},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.21881},
eprint = {2609.21881},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.21881},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Time-resolved JWST Retrieval Analysis of the Coldest Brown Dwarf: Temperature and Chemical Variations in WISE 0855-07
AU - Harshil Kothari
AU - Caroline V. Morley
AU - Brittany E. Miles
AU - Melanie J. Rowland
AU - Natasha Batalha
AU - Michael C. Cushing
AU - Andrew J. Skemer
AU - James Mang
AU - Brianna Lacy
AU - Johanna M. Vos
AU - Channon Visscher
AU - Adam C. Schneider
AU - Genaro Suarez
AU - Mikayla J. Wilson
AU - Allison M. McCarthy
PY - 2026
DA - 2026/09/18
PB - arXiv
DO - 10.48550/arxiv.2609.21881
UR - https://arxiv.org/abs/2609.21881
AB - WISE J0855-07 is the coldest known brown dwarf (estimated Teff~250 K), offering a rare opportunity to probe atmospheric physics in the temperature and mass regime that overlaps directly with exoplanets. At these temperatures, modest perturbations to the thermal structure and chemical abundances can produce measurable changes in the emergent mid-infrared spectrum, making time-resolved spectroscopy a powerful way to test whether the atmosphere is longitudinally and temporally homogeneous. Using James Webb Space Telescope NIRSpec/G395M time-series spectra spanning ~3 to 5.2 μm over 11 hr, we analyze every third spectrum from the dataset with a series of time-resolved atmospheric retrievals using the Brewster retrieval framework. Using this approach, we model epoch-to-epoch changes in the atmospheric state that drive the observed variability, including the thermal structure and key molecular abundances. From the time-series retrievals, we find that the primary source of the observed spectral variability is driven by the variations in the thermal structure, which range from ~1 to <100 K from epoch to epoch, particularly between the pressures of ~0.4 and 10 bar. In addition, changes in the abundances of CO, and possibly PH3 and CO2, further modulate the spectrum within specific molecular features. These measurements provide a retrieval-based view of atmospheric variability in an ultracold, planet-like object, directly constraining how thermal and chemical structure evolve on observable timescales.
ER -