GFADJUST

GFADJUST is a program, based on SPECTRUM code, that can be used to invert a stellar spectrum to determine oscillator strengths (gf values) for individual spectral lines. The gf values used in the linelist file luke.lst come from a number of sources. Some have been determined in the laboratory, others have been derived from theoretical calculations. The accuracy of these gf values varies widely from line to line; some are known to accuracies of 1% or better, others are off by an order of magnitude. The accuracy of the gf values is certainly one of the most important factors in determining whether or not a spectral synthesis calculation reproduces faithfully the spectrum of a star. Other factors include the accuracy with which the basic physical parameters have been determined for the star in question, the quality of the broadening parameters and theory, the validity of the LTE approximation, etc.

Within the limitations of those other factors, GFADJUST may be used to determine gf values from measurement of the spectrum of a well-studied star such as the sun. To determine the gf value for a particular spectral line, its equivalent width must be measured and included in the input linelist for GFADJUST. The format of this line list is identical to the ones used for both ABUNDANCE and BLACKWEL. GFADJUST also requires as input a stellar atmosphere model for the star in question and a microturbulent velocity. The output from GFADJUST has the following format:

Wavelength     Code     Log10(gf)

In addition to the caveats above, care must be taken to ensure that the spectral lines for which you are determining the gf values are unblended, or that you have adequately separated out the components of the blend. GFADJUST does not support isotopes, nor should it be used with lines with measurable hyperfine structure. Likewise, GFADJUST should not be used to determine the gf values for strong lines. Only the ``t'' switch may be used with GFADJUST(see § ).