{
  "abstract": "We present JWST NIRSpec and MIRI observations of the metal-poor T dwarf WISEA J155349.96+693355.2. The combined NIRSpec/prism plus MIRI/LRS spectrum (R ~ 100) provides 0.6-12 $μ$m spectroscopic coverage that reveals the presence of H$_2$O, CH$_4$, and NH$_3$ absorption features, enhanced collision-induced H$_2$ absorption, and weak or absent CO and CO$_2$ absorption, all indicators of a metal-poor low-temperature atmosphere. Comparison of the spectral data to a suite of atmosphere models yields an effective temperature $T_{\\rm eff}$ = 960$^{+28}_{-32}$ K and a solar-scaled metallicity of [M/H] = -1.16$^{+0.28}_{-0.25}$ dex. We find indications that the uncertain trigonometric parallax, likely subject to Lutz-Kelker bias, may be overestimated. Adopting the photometric distance yields a bolometric luminosity log$_{10}L_{bol}/L_{\\odot}$ = -5.29 $\\pm$ 0.10, from which we infer $T_{\\rm eff}$ = 974 $\\pm$ 56 K, consistent with the temperature derived via our atmospheric model fits. From the moderate-resolution (R ~ 3,000) NIRSpec/G395H spectrum, we measure a radial velocity of -163 $\\pm$ 5 km/s, which combined with the source's measured proper motion and estimated distance indicates a highly eccentric (e $\\geq$ 0.9) Galactic orbit consistent with an accreted halo object. The UVW kinematics of WISEA J155349.96+693355.2, its bulk metallicity, and its modest alpha enrichment ([$α$/Fe] = +0.15$^{+0.04}_{-0.06}$ dex) are all equivalent to stars identified in the Gaia-Enceladus Milky Way substructure, making it the first brown dwarf with kinematic and chemical evidence of association.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.29365",
  "author_total": 18,
  "authors": [
    {
      "name": "Aaron M. Meisner"
    },
    {
      "name": "Adam J. Burgasser"
    },
    {
      "name": "Chih-Chun Hsu"
    },
    {
      "name": "Sherelyn Alejandro Merchan"
    },
    {
      "name": "Jacqueline K. Faherty"
    },
    {
      "name": "Genaro Suárez"
    },
    {
      "name": "ZengHua Zhang"
    },
    {
      "name": "Roman Gerasimov"
    },
    {
      "name": "Christian Aganze"
    },
    {
      "name": "Nicolas Lodieu"
    },
    {
      "name": "Eileen C. Gonzales"
    },
    {
      "name": "Adam C. Schneider"
    },
    {
      "name": "Stanimir A. Metchev"
    },
    {
      "name": "Dan Caselden"
    },
    {
      "name": "Michael C. Cushing"
    },
    {
      "name": "Christopher A. Theissen"
    },
    {
      "name": "Jason J. Wang"
    },
    {
      "name": "Harshil Kothari"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/6y7wqzf9gfapx.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.29365",
  "fulltext_url": null,
  "id": "6y7wqzf9gfapx",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.29365",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.EP"
    ],
    [
      "arxiv",
      "astro-ph.GA"
    ],
    [
      "arxiv",
      "astro-ph.SR"
    ],
    [
      "openalex",
      "3103|Stellar, planetary, and galactic studies"
    ]
  ],
  "openalex": "W7214341755",
  "pdf_url": "https://arxiv.org/pdf/2609.29365",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-26",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/6y7wqzf9gfapx.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:25:12Z",
      "native_id": "2609.29365",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.29365"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.EP",
      "subfield": "planetary"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.SR",
      "subfield": "stellar"
    }
  ],
  "title": "JWST Observations of the Metal-poor T Dwarf WISEA J155349.96+693355.2: The First Brown Dwarf Associated with the Gaia-Enceladus Milky Way Substructure",
  "title_text": "JWST Observations of the Metal-poor T Dwarf WISEA J155349.96+693355.2: The First Brown Dwarf Associated with the Gaia-Enceladus Milky Way Substructure",
  "type": "preprint",
  "updated_at": "2026-10-30T12:25:12Z",
  "url": "https://research.draconitic.com/paper/6y7wqzf9gfapx",
  "venue": "arXiv",
  "versions": []
}