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Astron. Astrophys. 364, 876-878 (2000)

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1. Introduction

Helioseismology has revealed that the rotation regime in the Sun changes abruptly from latitude dependent in the convection zone to almost uniform in the radiation zone below. The top of the radiation zone is thus a region of strong vertical shear, and for this reason that layer has been called the tachocline (Spiegel & Zahn 1992). Acoustic sounding has shown also that some mild macroscopic mixing occurs in this region, to smoothen the composition gradient which, with microscopic diffusion only, would be somewhat steeper. Moreover, the Li depletion observed in solar-type stars can only be explained by some type of macroscopic transport between the convection zone and the depth where this fragile element is destroyed.

Among the possible mechanisms which may produce such mixing, a plausible one is the shear instability induced by the vertical rotation profile. In the present Note we shall verify whether this instability is able to play an effective role in the observed mixing.

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© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001