The Dyn-Atmo Survey: High-contrast Imaging Spectroscopy of the Substellar Companion HD 13724 B with the JWST NIRSpec IFU

@misc{hoch2026dynatmo,
  title = {{The Dyn-Atmo Survey: High-contrast Imaging Spectroscopy of the Substellar Companion HD 13724 B with the JWST NIRSpec IFU}},
  author = {Kielan K. W. Hoch and Alex Madurowicz and Evert Nasedkin and Emily Rickman and Daniella C. Bardalez Gagliuffi and James Mang and Caroline V. Morley and Christopher A. Theissen and William O. Balmer and Brendan P. Bowler and Emily Calamari and Henry Dennen and Jacqueline K. Faherty and Kyle Franson and Mark R. Giovinazzi and Lisseth Gonzales Quevedo and Elena Manjavacas and Piper Lentz and Klara Matuszewska and Ashley Messier and Marshall Perrin and Laurent Pueyo and Jean-Baptiste Ruffio and Kimberly Ward-Duong and Jerry W. Xuan},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.11827},
  eprint = {2609.11827},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.11827},
}

TY  - UNPB
TI  - The Dyn-Atmo Survey: High-contrast Imaging Spectroscopy of the Substellar Companion HD 13724 B with the JWST NIRSpec IFU
AU  - Kielan K. W. Hoch
AU  - Alex Madurowicz
AU  - Evert Nasedkin
AU  - Emily Rickman
AU  - Daniella C. Bardalez Gagliuffi
AU  - James Mang
AU  - Caroline V. Morley
AU  - Christopher A. Theissen
AU  - William O. Balmer
AU  - Brendan P. Bowler
AU  - Emily Calamari
AU  - Henry Dennen
AU  - Jacqueline K. Faherty
AU  - Kyle Franson
AU  - Mark R. Giovinazzi
AU  - Lisseth Gonzales Quevedo
AU  - Elena Manjavacas
AU  - Piper Lentz
AU  - Klara Matuszewska
AU  - Ashley Messier
AU  - Marshall Perrin
AU  - Laurent Pueyo
AU  - Jean-Baptiste Ruffio
AU  - Kimberly Ward-Duong
AU  - Jerry W. Xuan
PY  - 2026
DA  - 2026/09/10
PB  - arXiv
DO  - 10.48550/arxiv.2609.11827
UR  - https://arxiv.org/abs/2609.11827
AB  - We present the first spectral analysis from the JWST Cycle 3 GO Program #6362, the Dyn-Atmo Survey of dynamical-atmospheric benchmarks, characterizing the atmospheres of directly-imaged companions with dynamical masses and measured orbits. This program has obtained moderate-resolution spectra (R∼2700, 3-5μm) using the NIRSpec/G395H IFU. We observe the T4-dwarf companion, HD 13724 B, companion to a G-type star at a projected angular separation of 0''2. Updated orbital monitoring constrains the mass to 38.3±0.6 M_Jup, which we use as a Gaussian prior when inferring the atmospheric state. We fit the continuum-subtracted spectrum using the BT-SETTL, Sonora Diamondback, Sonora Flame Skimmer, and NEWERA-PHOENIX self-consistent model grids, together with petitRADTRANS atmospheric retrievals. We adopt bulk parameter values of T_eff=1150±195 K, log g=5.1±0.3 dex, [M/H]=0.4±0.4, log_10(K_zz)=6.33_−2.22^+2.59, and C/O=0.50±0.13 using a bayesian average across model grids. We find degeneracies in the models between surface gravity, metallicity, and K_zz for Sonora Diamondback and Flame Skimmer. The Flame Skimmer and NEWERA-PHOENIX vertical mixing strengths are incompatible, with Flame Skimmer finding a systematically lower value. The retrievals favor an atmosphere in chemical equilibrium, with enhanced metallicity and a solar C/O ratio, but with no detection of disequilibrium chemistry, and no detection of trace gases other than CH_4, CO_2, ^12CO and H_2O. Ultimately, we identify critical challenges in forward modeling continuum-subtracted G395H spectra in the low signal-to-noise regime. We find that including independent dynamical mass measurements better constrains atmospheric parameters, but degeneracies between self-consistent model parameters limit accurate atmospheric parameter inferences.
ER  -