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

Journal article, 2026

Although the migration of hot Jupiters is not yet fully understood, measurements of the projected spin-orbit angle lambda help shed light on the processes involved. Here we present Doppler tomography of three known hot Jupiters to determine their lambda 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 lambda = -85 .degrees 3 +/- 1 .degrees 7, second, HAT-P-57 A indicates practically no deviation of the planet's projected orbit from the host's equatorial plane with lambda=-0.4-1.9+1.4 degrees , and third, the XO-3 A system with the measured value of lambda=38-4+3 degrees 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.