{
  "abstract": "We present new JWST/NIRSpec IFU high contrast spectroscopic observations of the brown dwarf companion GJ 758 B. Extensive radial velocity monitoring of the primary has enabled high-precision measurements of the companion mass through characterization of their joint orbital dynamics. The combination of prior space- and ground-based photometry and spectroscopic observations in concert with a spectral model-independent mass makes this target an ideal benchmark for calibrating evolutionary models with known mass-age-luminosity degeneracies. A template-matching analysis on the NIRSpec/IFU data (F290LP,G395H; $λ\\in$ [2.87-5.27] $μ$m) detects the companion at the expected orbital position with incredible significance (265.2$σ$). Comprehensive spectral analysis including published datasets over a variety of different spectral model families reveal that an inference using a uniform radius prior is plagued by inaccurate posteriors. The atmospheric model degeneracy between metallicity, gravity, and clouds pull the inferred mass/gravity/radius to an unphysical portion of parameter space for all model families tested. A constrained inference with a gaussian prior on the mass can mitigate this issue but models without clouds still struggle to accurately reproduce the K-band photometry and result in mass inferences which are inconsistent with the dynamics. We explore modifying the spectral models with custom post-processed clouds and molecular abundance perturbations of ammonia and hydrogen sulfide. We find the best-fitting model includes clouds with no patchiness (hole fraction f$_\\mathrm{hole}$ = 0), a small fractional depletion in ammonia and moderate enhancement in hydrogen sulfide.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.11828",
  "author_total": 25,
  "authors": [
    {
      "name": "Alexander Madurowicz"
    },
    {
      "name": "Emily Rickman"
    },
    {
      "name": "Daniella Bardalez Gagliuffi"
    },
    {
      "name": "James Mang"
    },
    {
      "name": "Kim Ward-Duong"
    },
    {
      "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": "Kielan K. W. Hoch"
    },
    {
      "name": "Piper Lentz"
    },
    {
      "name": "Elena Manjavacas"
    },
    {
      "name": "Klara Matuszewska"
    },
    {
      "name": "Ashley Messier"
    },
    {
      "name": "Caroline V. Morley"
    },
    {
      "name": "Evert Nasedkin"
    },
    {
      "name": "Marshall Perrin"
    },
    {
      "name": "Laurent Pueyo"
    },
    {
      "name": "Jean-Baptiste Ruffio"
    },
    {
      "name": "Christopher A. Theissen"
    },
    {
      "name": "Jerry W. Xuan"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/2w3mcw73g47n7.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.11828",
  "fulltext_url": null,
  "id": "2w3mcw73g47n7",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.11828",
  "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": "W7212296971",
  "pdf_url": "https://arxiv.org/pdf/2609.11828",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-10",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/2w3mcw73g47n7.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:20:26Z",
      "native_id": "2609.11828",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.11828"
    }
  ],
  "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: JWST/NIRSpec spectroscopy of dynamical benchmark GJ 758 B",
  "title_text": "The Dyn-Atmo Survey: JWST/NIRSpec spectroscopy of dynamical benchmark GJ 758 B",
  "type": "preprint",
  "updated_at": "2026-10-30T12:20:26Z",
  "url": "https://research.draconitic.com/paper/2w3mcw73g47n7",
  "venue": "arXiv",
  "versions": []
}