{
  "abstract": "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$\\sim$2700, 3-5$μ$m) 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 $38.3\\pm0.6~M_{\\rm{Jup}}$, 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 $T_\\mathrm{eff}$=$1150\\pm$195 K, $\\log g$=5.1$\\pm0.3$ dex, [M/H]=0.4$\\pm$0.4, $\\log_{10}(K_{zz})$=6.33$_{-2.22}^{+2.59}$, and C/O=$0.50\\pm0.13$ 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$_{2}$, $^{12}$CO and H$_{2}$O. 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.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.11827",
  "author_total": 25,
  "authors": [
    {
      "name": "Kielan K. W. Hoch"
    },
    {
      "name": "Alex Madurowicz"
    },
    {
      "name": "Evert Nasedkin"
    },
    {
      "name": "Emily Rickman"
    },
    {
      "name": "Daniella C. Bardalez Gagliuffi"
    },
    {
      "name": "James Mang"
    },
    {
      "name": "Caroline V. Morley"
    },
    {
      "name": "Christopher A. Theissen"
    },
    {
      "name": "William O. Balmer"
    },
    {
      "name": "Brendan P. Bowler"
    },
    {
      "name": "Emily Calamari"
    },
    {
      "name": "Henry Dennen"
    },
    {
      "name": "Jacqueline K. Faherty"
    },
    {
      "name": "Kyle Franson"
    },
    {
      "name": "Mark R. Giovinazzi"
    },
    {
      "name": "Lisseth Gonzales Quevedo"
    },
    {
      "name": "Elena Manjavacas"
    },
    {
      "name": "Piper Lentz"
    },
    {
      "name": "Klara Matuszewska"
    },
    {
      "name": "Ashley Messier"
    },
    {
      "name": "Marshall Perrin"
    },
    {
      "name": "Laurent Pueyo"
    },
    {
      "name": "Jean-Baptiste Ruffio"
    },
    {
      "name": "Kimberly Ward-Duong"
    },
    {
      "name": "Jerry W. Xuan"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/4rfvsqjv9apfx.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.11827",
  "fulltext_url": null,
  "id": "4rfvsqjv9apfx",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.11827",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.EP"
    ],
    [
      "arxiv",
      "astro-ph.IM"
    ],
    [
      "arxiv",
      "astro-ph.SR"
    ],
    [
      "openalex",
      "3103|Stellar, planetary, and galactic studies"
    ]
  ],
  "openalex": "W7212226125",
  "pdf_url": "https://arxiv.org/pdf/2609.11827",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-10",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/4rfvsqjv9apfx.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:20:26Z",
      "native_id": "2609.11827",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.11827"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.IM",
      "subfield": "instrumentation-methods"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.EP",
      "subfield": "planetary"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.SR",
      "subfield": "stellar"
    }
  ],
  "title": "The Dyn-Atmo Survey: High-contrast Imaging Spectroscopy of the Substellar Companion HD 13724 B with the JWST NIRSpec IFU",
  "title_text": "The Dyn-Atmo Survey: High-contrast Imaging Spectroscopy of the Substellar Companion HD 13724 B with the JWST NIRSpec IFU",
  "type": "preprint",
  "updated_at": "2026-10-30T12:20:26Z",
  "url": "https://research.draconitic.com/paper/4rfvsqjv9apfx",
  "venue": "arXiv",
  "versions": []
}