calz_guess_ebv.pro
1.79 KB
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FUNCTION calz_guess_ebv,wave,flux_ratio,R_v=R_v
;+
; NAME:
; calz_guess_ebv,
; PURPOSE:
; Guess the value of E(B-V) to get a given stellar flux ratio
; EXPLANATION:
; based on calz_unred.pro by W. Landsman
; CALLING SEQUENCE:
; ebv=calz_guess_ebv(wave,flux_ratio,R_v=R_v)
; INPUT:
; WAVE - wavelength at which the flux ratio is given (Angstroms)
; FLUX_RATIO - flux ratio between unredened and redenned (observed) flux.
; OUTPUT:
; EBV - color excess E(B-V), scalar. positive if flux_ratio is >1 ,
; Note that the E(B-V) computed is for
; the stellar continuum, EBV(stars), which is related to the
; reddening derived from the gas, EBV(gas), via the Balmer
; decrement by EBV(stars) = 0.44*EBV(gas) according to Calzetti 2000.
; OPTIONAL INPUT KEYWORD:
; R_V - Ratio of total to selective extinction, default = 4.05.
; Calzetti et al. (2000) estimate R_V = 4.05 +/- 0.80 from optical
; -IR observations of 4 starbursts.
; EXAMPLE:
;
; print,calz_guess_ebv(10000.,1./0.98,R_v=R_v)
; 0.0116824
; NOTES:
;
; PROCEDURE CALLS:
; POLY()
; REVISION HISTORY:
; JPB 30 Jan 2024
;-
;flux_ratio=funred/flux must be >1 for positive E(B-V)
;print,calz_guess_ebv(10000.,1./0.98,R_v=R_v)
;wave_flux in AA
x = 10000.0/wave ;Wavelength in inverse microns
if N_elements(R_V) EQ 0 then R_V = 4.05
IF (wave GE 6300) AND (wave LE 22000) THEN $
klam = 2.659*(-1.857 + 1.040*x) + R_V
IF (wave GE 912) AND (wave LT 6300) THEN $
klam = 2.659*(poly(x, [-2.156, 1.509d0, -0.198d0, 0.011d0])) + R_V
;Calzetti 2000 equation is
;funred = flux*10.0^(0.4*klam*ebv)
;stop
;ebv=alog10(funred/flux)/0.4/klam
ebv=alog10(flux_ratio)/0.4/klam
RETURN,ebv
END