[daip] aips_gripe

[Eric Greisen]

Lincoln Greenhill writes:

 > I am concerned about the formula at the bottom of page 2 of the 
 > AIPS memo you refer to (#27).
 > 
 > For small velocities, for identical reference pixels in velocity
 > and frequency, and
 > for the radio definition of 
 > redshift, this formula does not approach the limit I expect
 > 
 > delta-velocity = speed-of-light * delta-nu / REST-FREQUENCY 
 > 
 > Why is that?
 > 

     Because you have made an error.

Vs - VR = -Dnu (C-VR) (N - NV) / NuR 

when NV = Nnu.  But

     (c-VR) / NuR = [c + C(NuR-Nu0)/Nu0] / NuR  = C/Nu0

as you expected.

Eric