Updated modelling framework reveals the orbital alignment of the hot Jupiter TOI-135 b

Star system: HD 2685 | Distance from the Sun: 644 light years

Understanding the orientation of an exoplanet's orbit relative to its host star's rotation provides essential clues about the system's past. A key method for measuring this alignment is the Rossiter-McLaughlin effect, which occurs when a transiting planet blocks different parts of a rotating star, creating a characteristic shift in the star's spectral lines. Researchers have now introduced an improved modelling framework within the exoplanet analysis code TLCM to better interpret these observations.

The team validated their updated model by applying it to nine well-studied planetary systems. They then used this framework to analyze HD 2685, also known as TOI-135, a hot, evolved star orbited by a hot Jupiter — a gas giant planet with an orbital period of about 4 days. By combining new HARPS radial velocity measurements taken during and outside of planetary transits with additional photometric data from six TESS observation sectors, the scientists were able to refine the orbital and system parameters.

The analysis successfully detected the Rossiter-McLaughlin effect for the system. The results indicate an intermediate sky-projected obliquity — the angle between the star's rotational axis and the planet's orbital plane — of approximately 55.6 degrees. This measurement remained stable across various tests, demonstrating the reliability of the updated TLCM framework for characterizing the orbital configurations of diverse exoplanetary systems.

Key findings
- Introduced an updated and validated Rossiter-McLaughlin modelling framework in the TLCM analysis code.
- Refined the planetary and orbital parameters for the hot Jupiter HD 2685 b (TOI-135 b).
- Successfully detected the Rossiter-McLaughlin effect in the TOI-135 system.
- Determined an intermediate sky-projected orbital obliquity of approximately 55.6 degrees for the planet.

Scientific study

A comprehensive Rossiter-Mclaughlin Modelling Framework in TLCM: Application to HD 2685 = TOI-135 system (external link)