Scaling Laws and Temperature Profiles for Solar and Stellar Coronal Loops with Non-uniform Heating

TL;DR

This paper develops analytical models for the temperature and scaling laws of solar and stellar coronal loops with various heating distributions, showing that temperature profiles are weakly dependent on heating location and that scaling laws are broadly applicable.

Contribution

It introduces analytical solutions for coronal loop temperature structures under diverse heating functions, extending the RTV scaling laws and analyzing the effects of heating concentration and variable loop diameter.

Findings

Temperature profile weakly depends on heating distribution.

Scaling laws remain valid across different heating functions, with proportionality constants varying.

Analytical solutions are stable and match numerical simulations.

Abstract

The bulk of solar coronal radiative loss consists of soft X-ray emission from quasi-static loops at the cores of Active Regions. In order to develop diagnostics for determining the heating mechanism of these loops from observations by coronal imaging instruments, I have developed analytical solutions for the temperature structure and scaling laws of loop strands for a wide range of heating functions, including footpoint heating, uniform heating, and heating concentrated at the loop apex. Key results are that the temperature profile depends only weakly on the heating distribution -- not sufficiently to be of significant diagnostic value -- and that the scaling laws survive for this wide range of heating distributions, but with the constant of proportionality in the RTV scaling law ($P_{0}L \thicksim T_{max}^3$) depending on the specific heating function. Furthermore, quasi-static analytical solutions do not exist for an excessive concentration of heating near the loop footpoints, a result in agreement with recent numerical simulations. It is demonstrated that a generalization of the solutions to the case of a strand with a variable diameter leads to only relatively small correction factors in the scaling laws and temperature profiles for constant diameter loop strands. A quintet of leading theoretical coronal heating mechanisms is shown to be captured by the formalism of this paper, and the differences in thermal structure between them may be verified through observations. Preliminary results from full numerical simulations demonstrate that, despite the simplifying assumptions, the analytical solutions from this paper are stable and accurate.