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(abridged) This paper aims at deciphering the dynamics of the envelope of arotating star when some angular momentum loss due to mass loss is present. Weespecially wish to know when the spin-down flow forced by the mass losssupersedes the baroclinic flows that pervade the radiative envelope of rotatingstars. We consider a Boussinesq fluid enclosed in a rigid sphere whose flowsare forced both by the baroclinic torque, the spin-down of an outer layer, andan outward mass flux. The spin-down forcing is idealized in two ways: either bya rigid layer that imposes its spinning down velocity at some interface or by aturbulent layer that imposes a stress at this same interface to the interior ofthe star. In the case where the layer is rigid and imposes its velocity, wefind that, as the mass-loss rate increases, the flow inside the star shows twotransitions: the meridional circulation associated with baroclinic flows isfirst replaced by its spin-down counterpart, while at much stronger mass-lossrates the baroclinic differential rotation is superseded by the spin-downdifferential rotation. In fact, we find three wind regimes: weak (or no wind),moderate, and strong. In the first case, the flow in the radiative envelope isof baroclinic origin. In the moderate case, the circulation results from thespin-down while the differential rotation may either be of baroclinic or ofspin-down origin, depending on the coupling between mass and angular momentumlosses. For fast rotating stars, our model says that the moderate wind regimestarts when mass loss is higher than ~1e-11 Msun/yr. In the strong wind case,the flow in the radiative envelope is mainly driven by angular momentumadvection. This latter transition depends on the mass and the rotation rate ofthe star, being around 1e-8 Msun/yr for a 3 Msun ZAMS star rotating at 200 km/saccording to our model.

Dynamics of the radiative envelope of rapidly rotating stars: Effects of spin-down driven by mass loss