Orbital alignment of four hot-Jupiter planets in binary star systems measured

Star system: KELT-2 A | Distance from the Sun: 439 light years

Four hot-Jupiter planets orbiting within binary star systems have been characterized for their orbital alignment. These massive gas planets, known as KELT-2 Ab, KELT-3 Ab, TOI-1333 Ab, and TOI-1789 Ab, were studied to understand how their orbits interact with their host stars. The study focused on whether these planets orbit in line with the rotation of their parent stars, providing insight into the complex dynamical processes occurring within multi-star systems.

Researchers employed the EXtreme PREcision Spectrograph at the Lowell Discovery Telescope to measure the Rossiter-McLaughlin effect. This technique tracks small changes in a star's light as a planet transits across its face, which reveals the angle between the planet's orbital plane and the star's equator. By combining these measurements with data from the TESS space telescope, the study confirmed that all four planets maintain aligned orbits.

These results were compared against existing theories of stellar obliquity, specifically the boundary known as the realignment break, which is set at approximately 6,193 degrees Kelvin. While models involving stellar von-Zeipel-Kozai-Lidov oscillations—a process where a companion star influences a planet's orbit—could not fully explain the distribution, the data suggests that a combination of orbital scattering and aligned populations better describes these systems.

Key findings
- All four studied hot-Jupiter planets in binary systems are aligned with their host stars.
- The stellar realignment temperature threshold is revised to 6,193 plus or minus 103 Kelvin.
- A pure von-Zeipel-Kozai-Lidov model cannot replicate observed planet orbital patterns.
- Combining scattering models with gravitational oscillations better fits the current population distribution.

Scientific study

CHIANTE I: Obliquity Measurements of Four High-Priority Ariel Targets in Binaries (external link)