Year: 2026
Type: article
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 (RM) effect in the hot-star/hot-Neptune system WASP-195 ( T eff = 6470 ± 100 K, v sin i ⋆ = 10.5 ± 1.1 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° ± 7°, 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 5 σ 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 RM effect, a feature that could help to widen the planet confirmation bottleneck while expanding the obliquity census of small planets around hot stars.
Source: The Astronomical Journal
Authors: Juan I. Espinoza-Retamal, Joshua N. Winn, Rafael Brahm, Luke B. Handley, Elise Koo, Caleb Lammers, Cristobal Petrovich, Guðmundur Stefánsson, Andrés Jordán, Xian-Yu Wang, Songhu Wang, Nicholas Saunders, Erik A. Petigura, Lauren M. Weiss, Ashley D. Baker, Theron W. Carmichael, Fei Dai, Jerry Edelstein, Jack Foley, Benjamin J. Fulton, Steven Giacalone, Steven R. Gibson, Samuel Halverson, Andrew W. Howard, Howard Isaacson, Emma McIntyre, Pranav H. Premnath, Maleah Rhem, Kodi Rider, Ryan A. Rubenzahl, Arpita Roy, Christopher Smith, Judah Van Zandt, Josh Walawender, Elina Y. Zhang, Jingyi Zhang
Institutions: Princeton University, Adolfo Ibáñez University, California Institute of Technology, University of Amsterdam, Netherlands Institute for Radio Astronomy, Indiana University, University of Chile, Yale University, University of California, Los Angeles, University of Notre Dame, University of Hawaiʻi at Mānoa, University of Hawaii System, University of California, Berkeley, University of California, Irvine, University of Kansas, Flatiron Institute, University of California, Santa Barbara, W.M. Keck Observatory
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Funders: National Science Foundation, National Aeronautics and Space Administration, W. M. Keck Foundation, Yale University, Purdue University, Princeton University, California Institute of Technology, University of Wisconsin-Madison, Space Telescope Science Institute, NASA Exoplanet Science Institute, Jet Propulsion Laboratory
OpenAlex ID: W7207861345