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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 3 ± 1 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover> <mml:mrow> <mml:mo>.</mml:mo> </mml:mrow> <mml:mrow> <mml:mtext>°</mml:mtext> </mml:mrow> </mml:mover> </mml:math> 7, second, HAT-P-57 A indicates practically no deviation of the planet’s projected orbit from the host’s equatorial plane with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>λ</mml:mi> <mml:mo>=</mml:mo> <mml:mspace width="0.1em"/> <mml:mtext>–</mml:mtext> <mml:mspace width="0.1em"/> <mml:mn>0</mml:mn> <mml:mo>.</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1.9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.4</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>°</mml:mo> </mml:math> , and third, the XO-3 A system with the measured value of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>λ</mml:mi> <mml:mo>=</mml:mo> <mml:mn>3</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>°</mml:mo> </mml:math> 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.