Description

This dereddening model uses the analytic formula for the mean extension law described in Cardelli, Clayton, & Mathis 1989, ApJ 345, 245:

A(lambda) = E(B-V) (aR_v+b) = 1.086 tau(lambda)

where tau(lambda) is the wavelength-dependent optical depth,

I(lambda) = I(0) exp[-tau(lambda)] ,

and a and b are computed using wavelength-dependent formulae which we will not reproduce here, for the wavelength range 1000 A - 3.3 microns. The relationship between the color excess and the column density is

E(B-V) = [ N_(Hgal) (10^20 cm^-2) ]/58.0

(Bohlin, Savage, & Drake 1978, ApJ 224, 132). The value of the ratio of total to selective extinction, R_v, is initially set to 3.1, the standard value for the diffuse ISM. The final model form is:

I(lambda) = I(0) exp[-N_(Hgal)(aR_v+b)/58.0/1.086]

This model should only be used as a multiplicative model:

sherpa> powlaw1d[con1](1.,2588.6,0.1)
sherpa> dered[dr](3.1,0.1)
sherpa> source 1 = con1*dr

This model provided courtesy of Karl Forster.

dered Parameters