Astron. Astrophys. 329, 792-798 (1998)

3. Density effects

The aim of this section is to examine the density dependence of the lineshape. According to equation (4), this dependence is contained in the maximum angular momentum , since , with Debye distance. Let us decompose the profile of equation (4) into two terms denoted and so that:

and let us put

where is the asymptotic Holtsmark profile, i.e:

which is the object of the next paragraph, is independent of the density. Hence, the density dependence comes from via the limit . We have calculated the latter contribution at various densities and temperatures.The results are reported in the Tables 1 to 3. It comes out from these tables that the influence of the density increases with the temperature, and that the density effect is meaningful only in the linecore and the near linewings ( Å). For greater than 8Å, the profile is linear in density, within an error less than , at densities below cm^-3. This result is accounted for by the convergence of sum (6) at a value of lower than .

Table 1. Values of at K and various densities (in cm^-3). Each dash is to be read as the closest number on the right hand side of the same line. stands for .

Table 2. Same as table 1 with K

Table 3. Same as Table 1 with K

At higher densities, gets smaller and the region of non-linearity enlarges. However, not too far in the line wings (detunings Å), is a good cut-off.

© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997
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