Stellar Obliquities in Long-period Exoplanet Systems (SOLES) I: The Spin-Orbit Alignment of K2-140 b

TL;DR

This paper measures the spin-orbit alignment of the long-period exoplanet K2-140 b, providing insights into its formation history and contributing to understanding the origins of different giant planet populations.

Contribution

It presents the first Rossiter-McLaughlin measurement for K2-140 b, a long-period giant planet, revealing an aligned system and advancing the study of planet formation theories.

Findings

K2-140 is an aligned system with a projected spin-orbit angle of 0.5±9.7 degrees.

The system suggests a dynamically cool formation history.

Supports the idea of different formation mechanisms for long-period and hot Jupiters.

Abstract

Obliquity measurements for stars hosting relatively long-period giant planets with weak star-planet tidal interactions may play a key role in distinguishing between formation theories for shorter-period hot Jupiters. Few such obliquity measurements have been made to date due to the relatively small sample of known wide-orbiting, transiting Jovian-mass planets and the challenging nature of these targets, which tend to have long transit durations and orbit faint stars. We report a measurement of the Rossiter-McLaughlin effect across the transit of K2-140 b, a Jupiter-mass planet with period $P=6.57$ days orbiting a $V=12.6$ star. We find that K2-140 is an aligned system with projected spin-orbit angle $\lambda=0.5\pm9.7$ degrees, suggesting a dynamically cool formation history. This observation builds towards a population of tidally detached giant planet spin-orbit angles that will enable a direct comparison with the distribution of close-orbiting hot Jupiter orbital configurations, elucidating the prevalent formation mechanisms of each group.