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Title: A Tendency Toward Alignment in Single-star Warm-Jupiter Systems

The distribution of spin–orbit angles for systems with wide-separation, tidally detached exoplanets offers a unique constraint on the prevalence of dynamically violent planetary evolution histories. Tidally detached planets provide a relatively unbiased view of the primordial stellar obliquity distribution, as they cannot tidally realign within the system lifetime. We present the third result from our Stellar Obliquities in Long-period Exoplanet Systems (SOLES) survey: a measurement of the Rossiter–McLaughlin effect across two transits of the tidally detached warm Jupiter TOI-1478 b with the WIYN/NEID and Keck/HIRES spectrographs, revealing a sky-projected spin–orbit angleλ=6.25.5+5.9°. Combining this new measurement with the full set of archival obliquity measurements, including two previous constraints from the SOLES survey, we demonstrate that, in single-star systems, tidally detached warm Jupiters are preferentially more aligned than closer-orbiting hot Jupiters. This finding has two key implications: (1) planets in single-star systems tend to form within aligned protoplanetary disks, and (2) warm Jupiters form more quiescently than hot Jupiters, which, in single-star systems, are likely perturbed into a misaligned state through planet–planet interactions in the post-disk-dispersal phase. We also find that lower-mass Saturns span a wide range of spin–orbit angles, suggesting a prevalence of planet–planet scattering and/or secular more » mechanisms in these systems.

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Publication Date:
Journal Name:
The Astronomical Journal
Page Range or eLocation-ID:
Article No. 104
DOI PREFIX: 10.3847
Sponsoring Org:
National Science Foundation
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