[fitsbits] frequency definitions

[Tom Kuiper]

Mike Nolan wrote:
> FREQREST should be the line frequency, but some writers put it in as the
> center of the band to make some piece of software happy: Some readers need it,
> but if you're doing a raw search, it doesn't make a lot of sense.
>   
We had a situation at CSO  recently in which we wanted two specific 
lines (one in each sideband) well positioned in the spectrometer.  We 
calculated a frequency that would do that.  That was the frequency which 
was Doppler-shifted to tune the receiver.  I would call that FREQREST, 
i.e., the frequency we wanted at the center of the band in the source 
rest frame.  However, I agree that this makes a velocity scale hard to 
interpret.

Regards

Tom