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arXiv · 2503.03745

Evidence for Primordial Alignment II: Insights from Stellar Obliquity Measurements for Hot Jupiters in Compact Multiplanet Systems

Brandon Thomas Radzom·Jiayin Dong·Malena Rice·Xian-Yu Wang·Kyle Hixenbaugh·George Zhou·Chelsea X. Huang·Songhu Wang
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Abstract

A significant fraction of hot Jupiters have orbital axes misaligned with their host stars' spin axes. The large stellar obliquities of these giants have long been considered potential signatures of high-eccentricity migration, which is expected to clear out any nearby planetary companions. This scenario requires that only isolated hot Jupiters be spin-orbit misaligned while those with nearby companions, which must have more quiescent histories, maintain low-obliquity orbits, assuming they formed aligned within their primordial protoplanetary disks. Investigations of this stellar obliquity-companionship connection, however, have been severely limited by the lack of hot Jupiters found in compact multi-planet systems. Here we present the sky-projected stellar obliquity ($λ$) of a hot Jupiter with a nearby inner companion recently discovered by NASA's Transiting Exoplanet Survey Satellite: TOI-5143 c. Specifically, we utilize the Doppler shadow caused by the planet's transit, enabled by the Rossiter-McLaughlin (RM) effect, to find that the planet is aligned with $λ=2.1 ^{+2.8}_{-2.7} \circ$. Of the exoplanets with RM measurements, TOI-5143 c becomes just the third hot Jupiter with a nearby companion, and is part of the 19th compact multi-planet single-star system, with an RM measurement. The spin-orbit alignment of these 19 systems provides strong support for primordial alignment, and thus implies that large obliquities are gained primarily due to post-disk dynamical interactions such as those inherent to high-eccentricity migration. As such, the observed spin-orbit alignment of hot Jupiters with nearby companions affirms that some fraction of these giants instead have quiescent origins.

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Brandon Thomas Radzom, Jiayin Dong, Malena Rice, Xian-Yu Wang, Kyle Hixenbaugh, George Zhou, Chelsea X. Huang, Songhu Wang. 2025-03-05. Evidence for Primordial Alignment II: Insights from Stellar Obliquity Measurements for Hot Jupiters in Compact Multiplanet Systems. https://doi.org/10.3847/1538-3881%2Fad9dd5

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