; file: exthminff_gray.pro = H-minus free-free extinction following Gray ; init: sometine in the 1990s for SSB2 ; last: Oct 2 2013 Rob Rutten ; note: originally from Gray 2nd edition 1992 p135 ff ; now 3rd edition 2005 function exthminff_gray,wav,temp,eldens ;+ ; ext=exthminff_gray(wav,temp,eldens) ; in: wav = wavelength [Angstrom] (number or array but then others number) ; temp = temperature [K] (number or array) ; eldens = electron density [electrons cm-3] (number or array) ; out: H-minus ff extinction [cm^2 per neutral hydrogen atom] ; assuming LTE ionization H/H-min ; NB: includes stimulated emission correction already! ;- ; answer no-parameter query if(n_params(0) lt 3) then begin print,'ext=exthminff_gray(wav,temp,eldens)' return,-1 endif ; read physics constants (cgs) @constants_cgs.idl ; other parameters ll=1.D0*wav theta=5040./temp elpress=eldens*kcgs*temp ; evaluate H-min free-free including stimulated emission = Gray 2005 p156 logll=alog10(ll) f0 = -2.2763 -1.6850*logll +0.76661*logll^2 -0.0533464*logll^3 f1 = 15.2827 -9.2846*logll +1.99381*logll^2 -0.142631*logll^3 f2 = -197.789 +190.266*logll -67.9775*logll^2 +10.6913*logll^3 $ -0.625151*logll^4 ltheta=alog10(theta) kappaff = 1.D-26*elpress*10^(f0+f1*ltheta+f2*ltheta^2) ; Gray (8.13) return,kappaff end