{
  "abstract": "Stellar obliquities provide important clues as to the formation and migration histories of planetary systems, but measurements remain scarce for Neptune-mass planets, especially those orbiting hot stars (above the Kraft break). Here we present observations of the Rossiter-McLaughlin effect in the hot-star/hot-Neptune system WASP-195 ($T_{\\rm eff}=6470\\pm100$ K, $v\\sin{i_\\star}=10.5\\pm1.1$ km s$^{-1}$) obtained with the Keck Planet Finder and NEID spectrographs. A joint analysis of these observations, archival photometry, and archival radial velocities yields a sky-projected stellar obliquity of $λ=-10\\pm7^\\circ$, consistent with spin-orbit alignment. This makes WASP-195 one of the few hot-star/hot-Neptune systems with a measured obliquity. Archival radial velocities from SOPHIE exclude Jupiter-mass planets within approximately 3 au at $5σ$ confidence. The aligned and nearly circular orbit is naturally consistent with a history of disk-driven migration, although coplanar high-eccentricity migration or Roche-lobe overflow cannot be ruled out. We also investigate why so few Neptunes around hot stars have measured obliquities. Their scarcity likely reflects a combination of the lower intrinsic occurrence of short-period Neptunes around hot stars and the difficulty of confirming planet candidates in this regime, where rapid stellar rotation broadens spectral lines and hampers conventional radial-velocity confirmation. Rapid rotation also increases the detectability of the Rossiter-McLaughlin effect, a feature that could help to widen the planet confirmation bottleneck while expanding the obliquity census of small planets around hot stars.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.02888",
  "author_total": 36,
  "authors": [
    {
      "name": "Juan I. Espinoza-Retamal"
    },
    {
      "name": "Joshua N. Winn"
    },
    {
      "name": "Rafael Brahm"
    },
    {
      "name": "Luke B. Handley"
    },
    {
      "name": "Elise Koo"
    },
    {
      "name": "Caleb Lammers"
    },
    {
      "name": "Cristobal Petrovich"
    },
    {
      "name": "Guðmundur Stefánsson"
    },
    {
      "name": "Andrés Jordán"
    },
    {
      "name": "Xian-Yu Wang"
    },
    {
      "name": "Songhu Wang"
    },
    {
      "name": "Nicholas Saunders"
    },
    {
      "name": "Erik A. Petigura"
    },
    {
      "name": "Lauren M. Weiss"
    },
    {
      "name": "Ashley D. Baker"
    },
    {
      "name": "Theron W. Carmichael"
    },
    {
      "name": "Fei Dai"
    },
    {
      "name": "Jerry Edelstein"
    },
    {
      "name": "Jack Foley"
    },
    {
      "name": "Benjamin J. Fulton"
    },
    {
      "name": "Steven Giacalone"
    },
    {
      "name": "Steven R. Gibson"
    },
    {
      "name": "Samuel Halverson"
    },
    {
      "name": "Andrew W. Howard"
    },
    {
      "name": "Howard Isaacson"
    },
    {
      "name": "Emma McIntyre"
    },
    {
      "name": "Pranav H. Premnath"
    },
    {
      "name": "Maleah Rhem"
    },
    {
      "name": "Kodi Rider"
    },
    {
      "name": "Ryan A. Rubenzahl"
    },
    {
      "name": "Arpita Roy"
    },
    {
      "name": "Christopher Smith"
    },
    {
      "name": "Judah Van Zandt"
    },
    {
      "name": "Josh Walawender"
    },
    {
      "name": "Elina Y. Zhang"
    },
    {
      "name": "Jingyi Zhang"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/4sadfbpdtzx2w.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.02888",
  "fulltext_url": null,
  "id": "4sadfbpdtzx2w",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.02888",
  "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",
      "3103|Stellar, planetary, and galactic studies"
    ]
  ],
  "openalex": "W7207861345",
  "pdf_url": "https://arxiv.org/pdf/2609.02888",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-07",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/4sadfbpdtzx2w.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:27:37Z",
      "native_id": "2609.02888",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.02888"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.EP",
      "subfield": "planetary"
    }
  ],
  "title": "POSEIDON III: The Aligned Orbit of the Hot Neptune Around the Hot Star WASP-195",
  "title_text": "POSEIDON III: The Aligned Orbit of the Hot Neptune Around the Hot Star WASP-195",
  "type": "preprint",
  "updated_at": "2026-10-30T12:27:37Z",
  "url": "https://research.draconitic.com/paper/4sadfbpdtzx2w",
  "venue": "arXiv",
  "versions": []
}