Determination of mass-loss rates from early-type stars on the basis of 'log(W1)-log(W1 0)' diagrams

Using realistic expressions for the velocity and opacity distributions in rapidly expanding atmospheres, the author presents numerical results for the first order moment W[SUB]1[/SUB] of a P Cygni line profile calculated as a function of the parameter W[SUB]1[/SUB][SUP]0[/SUP] â Mn(level), where Mrepresents the mass-loss rate and n(level) the average fractional abundance of the relevant ion. The calculations clearly show that the resulting "log(W[SUB]1[/SUB]) - log(W[SUB]1[/SUB][SUP]0[/SUP])" curves depend almost essentially on the opacity distribution and that for unsaturated P Cygni line profiles the relation W[SUB]1[/SUB] â Mn(level) holds irrespective of the both distributions. For W[SUB]1[/SUB] ⪠0.24, the line profiles become saturated and the first order moment W[SUB]1[/SUB] does not provide anymore accurate information on the mass-loss rate. This technique of mass-loss determination and that which consists in fitting observed line profiles with theoretical ones are compared.