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[fitsbits] frequency definitions
I'd like to get it clear in my mind what the various frequency
definitions are. Is the following right? If there is a place where all this is clearly laid ou, please refer me to that. CRVALx - the value corresponding to the pixel CRPIXx in frame defined by CTYPEx. OBSFREQ - the actual frequency to which the receiver is tuned corresponding to the center of the IF. RESTFREQ - the receiver frequency (corresponding to the center of the IF) in the reference frame defined in TTYPEx. ( Vdop ) OBSFREQ = RESTFREQ * ( 1 - ------) ( c ) where Vdop is the velocity of the reference frame with respect to the observer. If we assume that CRPIXx is the pixel corresponding to the center of the IF, then CRVALx = RESTFREQ if CTYPEx = FREQ-LSR, CRVALx = OBSFREQ if CTYPEx = FREQ-OBS What is the difference between FREQ-OBS and FREQREST? Thanks and regards Tom |
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