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The co-moving frame radiative transfer equation for spherically
symmetric flows can be written
as :

We set *c*=1; is the velocity; and
is the usual Lorentz factor.
Equation is a integro-differential equation, since the
emissivity contains J_ , the zeroth angular moment of
I_ :

and
where is the source function, is the absorption
opacity, and is the scattering opacity.
With
the assumption of time-independence and a monotonic velocity field Eq. 1 becomes a boundary-value problem in
the spatial coordinate and an initial value problem in the frequency
or wavelength coordinate. The equation can be written in operator form
as:

where is the lambda-operator.

*Peter H. Hauschildt*

*4/27/1999*