The purpose of this paper is to give detailed systematic considerations to clarify and provide insights and a qualitative guide into the role of the azimuthal wind flow in the stellar-rotation braking mechanism. For this purpose, we make use of the Weber-Davis [Astrophys. J. 148, 217 (1967)] magnetohydrodynamic (MHD) version of Parker's [Astrophys. J. 128, 664 (1958)] stellar wind model. For the case when the magnetic field is primarily radial (as that near the surface of a star), the Weber-Davis [Astrophys. J. 148, 217 (1967)] "slow" magnetosonic critical point becomes Parker's [Astrophys. J. 128, 664 (1958)] sonic critical point, and the azimuthal wind flow can be approximated by corotation. Stellar rotation is shown to cause the sonic critical point to occur lower in the corona, and so the stellar wind experiences a stronger "afterburner" (as in an aircraft jet engine) action in the corona. Our results show that stellar rotation leads to considerably enhanced stellar wind acceleration even for moderate rotators like the sun. On the other hand, the stellar wind is shown to experience an immensely enhanced acceleration in a narrow shell near the star for strong rotators. This is underscored by the sonic critical point occurring considerably lower in the corona for strong rotators, hence supporting a huge afterburner action in the corona for such stars. For strong rotators, this sonic critical point is shown to be determined only by the basic stellar parameters such as mass M and angular velocity Omega, which signify the dominance of centrifugal and magnetic drivings in accelerating the stellar wind for such stars. Stellar rotation causes the physical throat section of the effective "de Laval" nozzle associated with the stellar wind flow to become narrower and the nozzle to also have a larger flare, indicative of an enhanced flow acceleration. The de Laval nozzle analogy does not, however, comply with the density drop in the stellar wind correctly. Thus, stellar rotation leads to tenuous and faster stellar wind flows without changes in the mass flux and hence enables protostars and strong rotators to lose their angular momentum quickly. Published under license by AIP Publishing.
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