Issue |
Astron. Astrophys. Suppl. Ser.
Volume 117, Number 1, May II 1996
|
|
---|---|---|
Page(s) | 189 - 195 | |
DOI | https://doi.org/10.1051/aas:1996101 | |
Published online | 15 May 1996 |
An efficient method for dealing with line haze in stellar spectra
Department of Physics and Astronomy, University of Victoria, Box 3055, MS7700, Victoria, B.C. V8W 3P6 Canada
Send offprint request to: Ana M. Larson
Received:
3
June
1995
Accepted:
7
October
1995
When analyzing any wavelength region, stellar spectroscopists must deal
with the multitude of weak lines which depress the true continuum and
thus form the pseudocontinuum. Calculating the effect of these lines,
known collectively as the “line haze,” under conventional synthetic
spectrum analysis is CPU intensive; an excessive amount of time is often
spent calculating the opacity profiles of lines which are too weak to
have even a cumulative effect on the line haze. We have developed a
method of identifying and eliminating these “ultraweak” lines from
synthetic spectrum computations. We treat the line opacity as a
perturbation to the continuum opacity and generate tables of equivalent
width coefficients which are a function of the model atmosphere,
species, excitation potential, and wavelength region. Through
interpolation of these tables and knowledge of the gf value for each
line, we rapidly and accurately calculate the equivalent width of any
line on the linear part of the curve of growth. We then determine the
cumulative line blocking as a function of equivalent width. Through the
use of this function and a specified line-blocking error, we eliminate
from further consideration all lines having little or no effect on the
pseudocontinuum. The reduction in the number of lines used in the
spectrum synthesis results in a significant savings in computation time.
We present the method for atomic and molecular lines in the
864-878 nm wavelength region, effective temperatures of 4000-6000 K,
of 1.5-4.5 (cgs units), and solar abundances.
Key words: methods: analytical / atomic data / molecular data / stars: atmospheres
© European Southern Observatory (ESO), 1996