Abstract
Our data base includes chromospherically active binaries for which Prot is known accurately from photometry of the starspot wave. The SU UMa binaries are hypothesized to have starspots, in which case Psuperoutburst = Pmigration.
Evolved binaries are shown to be in excellent agreement with the new circularization theory of Tassoul; the evolved star’s radius cleanly separates the eccentric from the circular orbits.
Several binaries with eccentric orbits appear to be in pseudosynchronous rotation, in agreement with theory, but two or three systems surprisingly show Prot = Porb and Prot ≠ Ppseudo.
About 20% of our sample rotate asynchronously, with ΔP > 10%. Tassoul’s new synchronization theory predicts that evolved stars (base of the giant branch or above) should rotate synchronously unless the Porb > 1 yr. The several examples of grossly asynchronous rotation in binaries with Porb ≈ 1 month (HD 181809, λ And AY Cet) are therefore a puzzle. We suggest differential rotation with depth as an explanation, in which a co-rotating latitude. This suggests using observed (surface) rotation as a probe of internal rotation profiles.
Differential rotation as a function of latitude is examined for a large number of stars, with the coefficient k deduced from the small differences between observed Prot and Porb i synchronously rotating systems; k decreases sharply with decreasing Rossby number Ro. This is contrary to the prediction of linear dynamo theory (k proportional to 1/Ro) but consistent with non-linear dynamo theory, which expects k to be nearly suppressed by extremely rapid rotation. For the SU UMa systems, k is 600 times smaller than the solar value k⊙ = 0.189.
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Hall, D.S., Henry, G.W. (1990). Circularization, Synchronization, and Differential Rotation in Chromospherically Active Binaries. In: İbanoğlu, C. (eds) Active Close Binaries. NATO ASI Series, vol 319. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-0679-2_24
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DOI: https://doi.org/10.1007/978-94-009-0679-2_24
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