The Orbital Architecture of Qatar-6: A Fully Aligned 3-Body System?

Abstract

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 $\lambda ={0.1\pm 2.6}^{\circ }$. 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 3-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.

17 pages, 7 figures, accepted to AJ

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