Orbital alignment of the hot Neptune planet orbiting WASP-195 confirmed

Researchers have measured the orbital alignment of a Neptune-mass planet around the hot star WASP-195. By observing the Rossiter-McLaughlin effect, the study confirms that the planet maintains a spin-orbit alignment, providing insight into the migration history of this specific planetary system and helping to fill a data gap regarding smaller planets orbiting stars hotter than the sun.

Star system: WASP-195 | Distance from the Sun: 1609 light years

The orbital characteristics of a Neptune-mass planet orbiting the hot star WASP-195 reveal a spin-orbit alignment, meaning the planet's orbital path is aligned with the rotation of its parent star. This discovery adds to the limited number of systems containing hot Neptunes around hot stars where researchers have successfully measured the angle between the stellar equator and the planetary orbital plane. Such measurements are essential for understanding how planetary systems form and how planets migrate from their birth locations to their current positions near their host stars.

To determine this alignment, observations focused on the Rossiter-McLaughlin effect. This phenomenon occurs when a planet transits its host star, causing a small, temporary shift in the spectral lines of the star as the planet blocks portions of the rotating stellar surface. By utilizing the Keck Planet Finder and NEID spectrographs to measure these changes, combined with existing radial velocity data and photometry, the researchers established the sky-projected obliquity, or the tilt of the orbit, at negative ten degrees with a margin of error of seven degrees. This suggests a history of disk-driven migration, although other mechanisms like high-eccentricity migration cannot be excluded.

The findings also help explain the general scarcity of data regarding Neptunes orbiting hot stars. Stars with higher temperatures often rotate rapidly, which causes their spectral lines to broaden, making it difficult for standard radial velocity methods to confirm the existence of smaller planets. However, because this rapid rotation also enhances the Rossiter-McLaughlin effect, the study suggests this method could be a key tool for expanding the census of Neptune-sized planets around these challenging host stars.

Key findings
The hot Neptune orbiting WASP-195 is confirmed to be in a spin-orbit aligned state.
The orbital alignment was measured using the Rossiter-McLaughlin effect through high-precision spectroscopy.
Archival data rules out the presence of additional Jupiter-mass planets within approximately 3 astronomical units of the star.
The orbital configuration supports theories of disk-driven migration for Neptune-mass planets in this system.
Rapid stellar rotation in hot stars serves as an advantage for detecting the Rossiter-McLaughlin effect, despite complicating planet confirmation.

Scientific study

POSEIDON III: The Aligned Orbit of the Hot Neptune Around the Hot Star WASP-195 (external link)