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vgabs, zvgabs: gaussian absorption line with sigma in km/s

A gaussian absorption line as a multiplicative model with sigma in km/s. The zvgabs variant includes redshift as a parameter.

$\displaystyle M(E) = exp\left(-\left(par3/(\sqrt{2\pi}(par2/c))\right) exp\left(-.5\left(\left(E-par1\right)/(par2/c)\right)^2\right)\right) $
where:

par1 line energy in keV.
par2 line width (sigma) in km/s.
par3 line depth in keV. The optical depth at line center is par3/(par2/c)/$\sqrt{2\pi}$.

For zvgabs the corresponding formula is:

$\displaystyle M(E) = exp\left(-\left(par3/(\sqrt{2\pi}(par2/c))\right) exp\left(-.5\left(\left(E(1+z)-par1\right)/(par2/c)\right)^2\right)\right) $
where:

par1 line energy in keV.
par2 line width (sigma) in km/s.
par3 line depth in keV. The optical depth at line center is par3/(par2/c)/$\sqrt{2\pi}$.
par4 $z$, redshift