| Issue |
A&A
Volume 711, July 2026
|
|
|---|---|---|
| Article Number | L10 | |
| Number of page(s) | 7 | |
| Section | Letters to the Editor | |
| DOI | https://doi.org/10.1051/0004-6361/202660175 | |
| Published online | 22 July 2026 | |
Letter to the Editor
Spin–spin coupling in stellar binaries
1
CFisUC, Departamento de Física, Universidade de Coimbra, 3004-516 Coimbra, Portugal
2
LTE, Observatoire de Paris, Université PSL, Sorbonne Université, CNRS, 75014 Paris, France
Received:
31
March
2026
Accepted:
26
May
2026
Abstract
Spin–orbit misalignment is increasingly observed in binary stars, but its origin remains uncertain. We study the secular spin dynamics of stellar binaries and derive the associated Cassini states. We isolate a spin–spin resonance that arises when the two stellar spin-precession frequencies become commensurate. This resonance can excite the obliquity of the secondary to high values even when the primary is only weakly tilted. Magnetic braking favors the formation of high-obliquity states, whereas tidal dissipation may suppress them. Spin–spin coupling may thus help explain the observed diversity of obliquities in young stellar binaries.
Key words: celestial mechanics / binaries: general / stars: kinematics and dynamics / stars: rotation
© The Authors 2026
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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