Rossiter-McLaughlin detection of the 9-month period transiting exoplanet HIP41378 d

TL;DR

This study measures the orbital obliquity of the long-period Neptune-sized exoplanet HIP41378 d using the Rossiter-McLaughlin effect, demonstrating ground-based follow-up potential for small, long-period planets.

Contribution

First measurement of obliquity for a 278-day period exoplanet, expanding RM technique application to long-period, Neptune-sized planets.

Findings

HIP41378 d has a prograde orbit with an obliquity of approximately 57 degrees.

No transit timing variations detected within the observational precision.

Confirms RM effect as a viable method for ground-based follow-up of small, long-period exoplanets.

Abstract

The Rossiter-McLaughlin (RM) effect is a method that allows us to measure the orbital obliquity of planets, which is an important constraint that has been used to understand the formation and migration mechanisms of planets, especially for hot Jupiters. In this paper, we present the RM observation of the Neptune-sized long-period transiting planet HIP41378 d. Those observations were obtained using the HARPS-N/TNG and ESPRESSO/ESO-VLT spectrographs over two transit events in 2019 and 2022. The analysis of the data with both the classical RM and the RM Revolutions methods allows us to confirm that the orbital period of this planet is 278 days and that the planet is on a prograde orbit with an obliquity of $\lambda$ = 57.1+26.4-17.9 degrees, a value which is consistent between both methods. HIP41378 d is the longest period planet for which the obliquity was measured so far. We do not detect transit timing variations with a precision of 30 and 100 minutes for the 2019 and 2022 transits, respectively. This result also illustrates that the RM effect provides a solution to follow-up from the ground the transit of small and long-period planets such as those that will be detected by the forthcoming ESA's PLATO mission.