2023AJ....165...65R

The evolutionary history of an extrasolar system is, in part, fossilized through its planets' orbital orientations relative to the host star's spin axis. However, spin-orbit constraints for warm Jupiters-particularly in binary star systems, which are amenable to a wide range of dynamical processes-are relatively scarce. We report a measurement of the Rossiter-McLaughlin effect, observed with the Keck/HIRES spectrograph, across the transit of Qatar-6 A b-a warm Jupiter orbiting one star within a binary system. From this measurement, we obtain a sky-projected spin-orbit angle λ = 0.°1 ± 2.°6. Combining this new constraint with the stellar rotational velocity of Qatar-6 A that we measure from TESS photometry, we derive a true obliquity $\psi ={21.82}_{-18.36}^{+8.86\circ} $-consistent with near-exact alignment. We also leverage astrometric data from Gaia DR3 to show that the Qatar-6 binary star system is edge-on (${i}_{B}={90.17}_{-1.06}^{+1.07\circ} $), such that the stellar binary and the transiting exoplanet orbit exhibit line-of-sight orbit-orbit alignment. Ultimately, we demonstrate that all current constraints for the three-body Qatar-6 system are consistent with both spin-orbit and orbit-orbit alignment. High-precision measurements of the projected stellar spin rate of the host star and the sky-plane geometry of the transit relative to the binary plane are required to conclusively verify the full 3D configuration of the system.