Effects of Stellar Rotation in Parker's Hydrodynamic Stellar Wind Model: How Protostars and Strong Rotators Lose their Angular Momentum Fast

TL;DR

This paper explores how stellar rotation influences Parker's stellar wind model, revealing a new critical point that accelerates wind flow and helps protostars and strong rotators shed angular momentum rapidly.

Contribution

It introduces a new hydrodynamic critical point caused by stellar rotation, altering wind acceleration and angular momentum loss mechanisms in stellar wind models.

Findings

A new critical point appears lower in the corona for rotating stars.

Stellar rotation causes faster, more tenuous winds without changing mass flux.

Enhanced wind acceleration aids rapid angular momentum loss in protostars.

Abstract

The effects of the stellar rotation and the consequent azimuthal stellar wind flow in Parker's [9] hydrodynamic stellar wind model are discussed. Of special interest is the emergence of a whole new hydrodynamic physics via a new critical point in the stellar wind flow, which supersedes the critical point in Parker's [9] hydrodynamic model. The effect of the stellar rotation is shown to cause the new critical point to occur lower in the corona, so the stellar wind experiences a stronger afterburner (as in an aircraft jet engine) action in the corona. For strong rotators, the new critical point is shown to occur at a fixed location for a given star, determined only by the basic stellar parameters like the mass M and the angular velocity, the variations in the stellar wind environment notwithstanding. The stellar rotation leads to stronger density fall-off and enhanced acceleration of the stellar wind at large distances from the star - this effect materializes even close to the star, for strong rotators. The stellar rotation causes the physical throat section of the effective de Laval nozzle associated with the stellar wind flow to become narrower, indicative of an enhanced flow acceleration. Thus, the stellar rotation leads to tenuous and faster stellar wind flows without change in the mass flux, and hence provides an efficient physical mechanism for protostars and strong rotators to lose their angular momentum quickly.