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Published October 1, 2015 | Published + Submitted
Journal Article Open

Magnetic Origins of the Stellar Mass-Obliquity Correlation in Planetary Systems

Abstract

Detailed observational characterization of transiting exoplanet systems has revealed that the spin-axes of massive M ≳ 1.2M_☉ stars often exhibit substantial misalignments with respect to the orbits of the planets they host. Conversely, lower-mass stars tend to only have limited obliquities. A similar trend has recently emerged within the observational data set of young stars' magnetic field strengths: massive T-Tauri stars tend to have dipole fields that are ~10 times weaker than their less-massive counterparts. Here we show that the associated dependence of magnetic star–disk torques upon stellar mass naturally explains the observed spin–orbit misalignment trend, provided that misalignments are obtained within the disk-hosting phase. Magnetic torques act to realign the stellar spin-axes of lower-mass stars with the disk plane on a timescale significantly shorter than the typical disk lifetime, whereas the same effect operates on a much longer timescale for massive stars. Cumulatively, our results point to a primordial excitation of extrasolar spin–orbit misalignment, signalling consistency with disk-driven migration as the dominant transport mechanism for short-period planets. Furthermore, we predict that spin–orbit misalignments in systems where close-in planets show signatures of dynamical, post-nebular emplacement will not follow the observed correlation with stellar mass.

Additional Information

© 2015. The American Astronomical Society. Received 2015 April 29; accepted 2015 August 10; published 2015 September 24. We would like to thank Fred Adams, Heather Knutson, and Dave Stevenson for enlightening conversations. C.S. acknowledges funding from the NESSF15 Graduate Fellowship in Earth and Planetary Science. We would additionally like to thank an anonymous reviewer, whose comments led to an improved manuscript. This research is based in part upon work supported by NSF grant AST 1517936.

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Published - Spalding_2015p82.pdf

Submitted - 1508.02365v1.pdf

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August 22, 2023
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