AN EFFICIENT METHOD FOR DEALING WITH LINE HAZE IN STELLAR SPECTRA

When analyzing any wavelength region, stellar spectroscopists must dea l with the multitude of weak lines which depress the true continuum an d thus form the pseudocontinuum. Calculating the effect of these lines , known collectively as the ''line haze,'' under conventional syntheti c spectrum analysis is CPU intensive; an excessive amount of time is o ften spent calculating the opacity profiles of lines which are too wea k to have even a cumulative effect on the line haze. We have developed a method of identifying and eliminating these ''ultraweak'' lines fro m synthetic spectrum computations. We treat the line opacity as a pert urbation to the continuum opacity and generate tables of equivalent wi dth coefficients which are a function of the model atmosphere, species , excitation potential, and wavelength region. Through interpolation o f these tables and knowledge of the gf value for each line, we rapidly and accurately calculate the equivalent width of any line on the line ar part of the curve of growth. We then determine the cumulative line blocking as a function of equivalent width. Through the use of this fu nction and a specified line-blocking error, we eliminate from further consideration all lines having little or no effect on the pseudocontin uum. The reduction in the number of Lines used in the spectrum synthes is results in a significant savings in computation time. We present th e method for 314000 atomic and molecular lines in the 864-878 nm wavel ength region, effective temperatures of 4000-6000 K, log g of 1.5-4.5 (cgs units), and solar abundances.