An algorithm for calculating a speed-dependent Lorentzian profile

We present an algorithm for calculating speed-dependent Lorentzian profiles . Specifically, we show that the sum of two simple Lorentzians, subject to certain constraints, accurately reproduces a Lorentzian profile with a spee d-dependent broadening. Further, the algorithm may be used in more complica ted lineshapes in which the speed-dependent Lorentzian is embedded. The ben efits resulting from this construction are simplicity of form, the ability to use the form in further symbolic manipulations, and the use of preexisti ng fast computer codes for the evaluation of the function. Such practical c onsiderations make it possible to use speed-dependent lineshapes in applica tions such as atmospheric modeling, which demand accurate but computational ly efficient absorption curves. In addition, several biases or problems, th at occur when speed-dependent experimental profiles are fitted with a simpl e Lorentzian, are discussed. (C) 1999 Academic Press.