Definition of the Physical Problems Connected with Extended Atmospheres

Abstract

The necessity of carefully defining the phenomenological basis for classification of atmospheres as being “extended” is emphasized, and four alternative bases for such classification are suggested (1) the necessity to include curvature terms; (2) the presence of an ejected shell surrounding a central star; (3) an observational discrepancy between predicted and observed density gradient; (4) an anomaly between predicted and observed phenomena in stars with “dynamic” atmospheres such as cepheids. A number of physical problems connected with the presence of an extended stellar atmosphere are then categorized according to these alternative bases.