Hydrogen lines provide an important diagnostic tool for determining
fundamental stellar parameters like effective temperature or gravity.
This diagnostic means is mainly facilitated by the fact that the line
broadening is almost completely determined by Linear Stark effect. A
very successful theoretical description of this crucial broadening
mechanism has been developed by Vidal et al. (1973, and
references therein) and their tables have been in wide use since then.
Unfortunately, the tables cover only the first four lines of the Balmer
and Lyman series, which is rather limiting in lieu of the spectral
coverage obtainable with current detectors and space experiments.
Despite more elaborate broadening theories having been developed only
recently has a set of tables been computed that is applicable to stellar
envelopes (Stehlé 1994, 1996) and that extends to lines other than
and 
.
These new tabulations are based on the Model Microfield Method (or MMM,
Frisch & Brissaud 1971), which should be more accurate than VCS for
taking temporal statistics between the perturbers into account.
Regrettably, with a lowest temperature of 10000K, and only two
decades in electron density, the size of the Stehlé tables seriously
restricts their application. Fortunately, for many astrophysical
purposes where Doppler broadening is significant the differences between
VCS and MMM appear to be extremely small. Napiwotzki & Rauch (1994),
who used similar Stark broadening calculations by Schöning, could not
find significant differences between spectra computed with either method
for a wide range of stellar parameters (
K). The
Schöning calculations are not strict MMM calculations, however, but
only a simplified approximation to MMM. The differences to Stehlé
seem to be small (cf. Stehlé Fig. 2 (click here) and Schöning Fig. 1 (click here)) and in the
sense which should increase the deviations from VCS.
Having had a pressing need to analyze Paschen lines (Lemke & Venn 1996) and realizing that VCS published their computer code, we felt that after 25 years the VCS tables are still useful and should be extended to higher lines. No intention was made, however, to improve on or modify the VCS description as it was laid out in VCS 1973.
In the present paper we announce the availability of VCS tables for the Lyman, Balmer, Paschen, and Brackett series up to n=22, computed with the original program.