A generalized method for deriving mass-loss rates: The first order moment of unsaturated P Cygni line profiles |
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| Authors: | J Surdej |
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| Institution: | (1) Institut d'Astrophysique, Université de Liège, Belgium |
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| Abstract: | For the case of optically thin lines, we show that the relation existing between the first order momentW
1  (E( )/E
c
–1)(–12)d of a P Cygni profile and the quantityMn(level), whereM is the mass-loss rate of the central star andn(level) the fractional abundance of the ion under study, is in fact independent of any Sobolev-type approximations used for the transfer of line radiation, contrary to what has been assumed in some previous works (Castoret al., 1981; Surdej, 1982). Consequently, all results established in the context of  very rapidly expanding atmospheres and mainly referring to the non-dependence ofW
1 vs various physical (underlying photospheric absorption line, limb darkening, etc.) and geometrical (velocity fieldv(r), etc.) effects remain unchanged for arbitrary (e.g non-Sobolev type) outward-accelerating velocity laws.Whenever applied with caution, Equation (50) thus provides a very powerful means of deriving mass-loss rates—with a total uncertainty less than 60 percent—from the measurementW
1 of unsaturated P Cygni profiles observed in the spectrum of early—as well as late—type stars, quasars, etc. |
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| Keywords: | |
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