{
  "abstract": "Ultra-hot Jupiters are a rare yet valuable subset of exoplanets that can help elucidate both the internal properties of their host stars as well as the orbital evolution of close-in planets. An extreme among extremes, TOI-2109 b is a super-Jupiter ($1.347 \\pm 0.047 R_{\\rm Jup}$, $5.02 \\pm 0.75 M_{\\rm Jup}$) with the shortest orbital period (0.67247479 $\\pm$ 0.00000028 days) and the fastest predicted orbital decay rate of any known giant planet. Previous observations hinted at a quadratic long-term trend in the transit timing variations (TTVs) consistent with orbital decay, as well as short-term sinusoidal TTVs consistent with a near-resonant planetary companion that would indicate a dynamically quiescent migration pathway. Here, we combine archival ground-based, TESS, and CHEOPS photometry with new transit and eclipse data from HST and JWST to update the TTV analysis. We find very strong evidence for sinusoidal TTVs over a linear ephemeris ($Δ$BIC of 33.6), consistent with a nearby planetary companion as suggested by J.-V. Harre et al. 2024, and rule out several non-planetary scenarios that could explain the sinusoidal TTVs. We also find strong evidence of a quadratic TTV trend ($Δ$BIC of 6.75) consistent with an orbital decay rate of -3.46 $\\pm$ 1.17 ms/yr and a stellar tidal quality factor of 2.13$^{+1.18}_{-0.61} \\times10^7$, though we cannot rule out line-of-sight acceleration as the cause of the quadratic trend. If our results are confirmed, TOI-2109 b would be the only known exoplanet besides WASP-12 b with a decaying orbit and the most extreme of an ultra-rare class of close-in giant planets with nearby companions.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.26894",
  "author_total": 12,
  "authors": [
    {
      "name": "Michael Greklek-McKeon"
    },
    {
      "name": "Julie Inglis"
    },
    {
      "name": "Nicole L. Wallack"
    },
    {
      "name": "Shreyas Vissapragada"
    },
    {
      "name": "Ian Wong"
    },
    {
      "name": "John R. T. Allen"
    },
    {
      "name": "Yayaati Chachan"
    },
    {
      "name": "Fei Dai"
    },
    {
      "name": "Guangwei Fu"
    },
    {
      "name": "Tiffany Kataria"
    },
    {
      "name": "Thaddeus D. Komacek"
    },
    {
      "name": "Johanna K. Teske"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/1nmvf5gbqvxwt.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.26894",
  "fulltext_url": null,
  "id": "1nmvf5gbqvxwt",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.26894",
  "language": null,
  "licence": "CC-BY-NC-ND-4.0",
  "licence_label": "CC BY-NC-ND 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by-nc-nd/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.EP"
    ],
    [
      "openalex",
      "3103|Stellar, planetary, and galactic studies"
    ]
  ],
  "openalex": "W7214160592",
  "pdf_url": "https://arxiv.org/pdf/2609.26894",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-22",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/1nmvf5gbqvxwt.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:23:56Z",
      "native_id": "2609.26894",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.26894"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.EP",
      "subfield": "planetary"
    }
  ],
  "title": "JWST and HST Confirm Transit Timing Variations for the Ultra-Hot Jupiter TOI-2109 b",
  "title_text": "JWST and HST Confirm Transit Timing Variations for the Ultra-Hot Jupiter TOI-2109 b",
  "type": "preprint",
  "updated_at": "2026-10-30T12:23:56Z",
  "url": "https://research.draconitic.com/paper/1nmvf5gbqvxwt",
  "venue": "arXiv",
  "versions": []
}