Line Profiles of Faculae and Pores

Abstract

Historically, attempts to model the temperature structure of faculae have generally suffered from a rather basic contradiction. Models which were based on center to limb measurements of the continuum contrast of faculae disagree with models that are based on measurements of line profiles in faculae. The “continuum” models predict line weakenings which are of larger amplitude than what is observed, and the “line profile” models predict a continuum contrast that is less than what is observed. Chapman (1976) discusses this problem in some detail. It is the purpose of this paper to show that there is a fundamental reason for this historical contradiction between line profile measurements and continuum contrast measurements: The line profile and the continuum contrast of a given facular are both a function (the two functions are different) of the size of that facula. The first indication of this fact was given by Frazier (1971). Figure 1 shows the contrast of faculae in the core of the line Fe Iλ 525. 0 nm, and in the continuum, as a function of the observed magnetic flux. One can see immediately that the contrast in each channel depends on φ in a much different manner. Therefore, one can conclude that the shape of the entire line profile will vary as a function of φ. On the basis of Figure 1, we must expect that this variation of the line profile will be continuous from infinitesimally small faculae up through very large faculae, and indeed, all the way up to pores.