{
  "abstract": "Using TESS photometry and 147 HARPS radial velocities, we confirm two extremely irradiated, volatile-rich sub-Neptunes near the lower edge of the Neptunian desert: TOI-426 b and TOI-1839 b, orbiting the solar-type stars HD 34390 and TYC 304-865-1. We modelled stellar activity with shared-timescale and multidimensional Gaussian processes. The planets have orbital periods of approximately 1.32 and 1.42 days, radii of $2.19\\pm0.09$ and $2.27\\pm0.10$ Earth radii, and masses of $6.7\\pm1.8$ and $7.10\\pm0.78$ Earth masses, respectively. They receive approximately 1700 and 1050 times Earth's irradiation, yet their densities require substantial volatile content. We also detect a transiting sub-Neptune, TOI-1839 c, at approximately 4.02 days and a giant companion, TOI-426 c, with a period of $235.8^{+9.2}_{-8.5}$ days and a minimum mass of $444^{+18}_{-17}$ Earth masses, assuming a circular orbit. Interior-structure and atmospheric-escape models yield mass-loss timescales of 1-100 Myr for hydrogen/helium envelopes, compared with 100-1000 Gyr for water-dominated envelopes, favouring a steam-world interpretation for all three transiting planets. A population analysis reveals a striking excess of detected outer giant companions to low-mass sub-Neptunes near the desert edge, where high-eccentricity tidal migration is expected to circularize surviving planets: 36% (9/25) within the tidal survival band versus 6% (9/148) outside it (Fisher exact test $p=1.4\\times10^{-4}$). This excess is robust to changes in sample selection and companion definitions. The survival of these volatile-rich planets challenges a boundary set solely by evaporation of primordial hydrogen/helium envelopes, while the companion excess supports an important role for high-eccentricity tidal migration in shaping the lower desert edge.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.05413",
  "author_total": 29,
  "authors": [
    {
      "name": "A. Castro-González"
    },
    {
      "name": "O. Barragán"
    },
    {
      "name": "D. J. Armstrong"
    },
    {
      "name": "A. Aguichine"
    },
    {
      "name": "V. Bourrier"
    },
    {
      "name": "D. Ehrenreich"
    },
    {
      "name": "E. X. Tao"
    },
    {
      "name": "J. Lillo-Box"
    },
    {
      "name": "M. R. Standing"
    },
    {
      "name": "S. G. Sousa"
    },
    {
      "name": "E. Delgado-Mena"
    },
    {
      "name": "A. Moya"
    },
    {
      "name": "V. Adibekyan"
    },
    {
      "name": "M. Lendl"
    },
    {
      "name": "C. Hellier"
    },
    {
      "name": "S. B. Howell"
    },
    {
      "name": "E. Furlan"
    },
    {
      "name": "C. Ziegler"
    },
    {
      "name": "A. C. M. Correia"
    },
    {
      "name": "K. Cui"
    },
    {
      "name": "P. Figueira"
    },
    {
      "name": "J. M. Jenkins"
    },
    {
      "name": "M. A. Fetzner Keniger"
    },
    {
      "name": "B. Merín"
    },
    {
      "name": "A. Osborn"
    },
    {
      "name": "L. Parc"
    },
    {
      "name": "F. Pepe"
    },
    {
      "name": "P. J. Wheatley"
    },
    {
      "name": "J. N. Winn"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/985g7dfqxa3hs.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.05413",
  "fulltext_url": null,
  "id": "985g7dfqxa3hs",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.05413",
  "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"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2609.05413",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-10",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/985g7dfqxa3hs.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:20:26Z",
      "native_id": "2609.05413",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.05413"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.EP",
      "subfield": "planetary"
    }
  ],
  "title": "Two extremely irradiated volatile-rich sub-Neptunes with companions in the TOI-426 and TOI-1839 systems: Insights into arrival and survival near the lower edge of the Neptunian desert",
  "title_text": "Two extremely irradiated volatile-rich sub-Neptunes with companions in the TOI-426 and TOI-1839 systems: Insights into arrival and survival near the lower edge of the Neptunian desert",
  "type": "preprint",
  "updated_at": "2026-10-30T12:20:26Z",
  "url": "https://research.draconitic.com/paper/985g7dfqxa3hs",
  "venue": "arXiv",
  "versions": []
}