Constraints Imposed by the Square-Root Spin-down Law on Coronal Wind Parameters

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Thursday, March 7, 2019

We derive an explicit expression for the coronal wind mass-loss rate. This result is based on a currently used generalized torque formula (per unit rotational velocity) expressed as a product of known monomials, separately for the magnetic field and the mass-loss rate.

Graph depicting Coronal Wind Mass-Loss Rate
Distribution of coronal wind parameters.

The latter is assumed here to be given by an unknown monomial power of the magnetic field. This yields a generalized torque dependent solely on the magnetic field that must yield the Square-Root Spin-down Law. A monomial dynamo relation, defining the rotational power index for the field (dynamo index), is derived from the congruity of the decay with age of the observed CaII emission luminosity (with an arbitrary magnetic field power dependence) with the decay with age of the rotational velocity and allows one to express the mass-loss rate power index in terms of the dynamo index. We apply this constraining equation to a variety of observations. We find, even though there is considerable scatter in the data, that there is sufficient observational evidence for the reality of a linear Dynamo relation that leads to a linear temporal decay of the mass-loss rate.

Publication Name: Astrophysical Journal

First HAO Author's Name: Andrew Skumanich