View Single Post
  #9  
Old May 6th 09, 08:10 PM posted to sci.astro.fits
Bob Garwood
external usenet poster
 
Posts: 8
Default [fitsbits] frequency definitions

I think I'd avoid that usage and invent another keyword for that
purpose. It's a useful thing to make note of - i.e. that's the
frequency we're using to do the updates necessary for dopper tracking,
but as you say, it would generate a not particularly useful velocity
scale and readers who are unfamiliar with the CSO and that use will be
likely to make that mistake, which I think is a bad thing.

And I'm sorry for mis-interpreting you use of "FREQ-OBS". In
retrospect, that's a CTYPEn value and Arnold's reply is useful. In the
SDFITS convention, OBSFREQ is explicitly defined to be in the observers
frame of reference independent of the CTYPEn value.

-Bob

Tom Kuiper wrote:
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
_______________________________________________
fitsbits mailing list

http://listmgr.cv.nrao.edu/mailman/listinfo/fitsbits


Ads