Aligned, Misaligned, and Polar Orbits of Hot Jupiters: Measuring Spin-orbit Angles via Doppler Tomography with HARPS-N

Abstract Although the migration of hot Jupiters is not yet fully understood, measurements of the projected spin–orbit angle λ help shed light on the processes involved. Here we present Doppler tomography of three known hot Jupiters to determine their λ orientation: HAT-P-49 b, HAT-P-57 A b, and XO-3 A b. Our analysis explores the impact of cross-correlation processing methods on the detectability and characterization of the planet’s Doppler shadow using up to three independent routines for cross-correlation functions extraction; those being: Yabi , iSpec , and IRAF . After accounting for differences among the results obtained with the various routines, we report: first, the HAT-P-49 system is a case of a hot Jupiter on a polar orbit with λ = –85 . ° 3 ± 1 . ° 7, second, HAT-P-57 A indicates practically no deviation of the planet’s projected orbit from the host’s equatorial plane with λ = – 0 . 4 − 1.9 + 1.4 ° , and third, the XO-3 A system with the measured value of λ = 3 8 − 4 + 3 ° lies in between an aligned and a perpendicular orientation, which is a less populated region of the spin–orbit distribution. Our findings highlight both the diversity of spin–orbit angles among close-in giant planets and the potential discrepancies in their measurement that can arise from different approaches to constructing the cross-correlation functions.