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ImagFreq - The image sideband equivalent of the rest frequency

Description:
This is a read-only attribute giving the frequency which corresponds to the rest frequency but is in the opposite sideband.

The value is calculated by first transforming the rest frequency (given by the RestFreq attribute) from the standard of rest of the source (given by the SourceVel and SourceVRF attributes) to the standard of rest of the observer (i.e. the topocentric standard of rest). The resulting topocentric frequency is assumed to be in the same sideband as the value given for the DSBCentre attribute (the "observed" sideband), and is transformed to the other sideband (the "image" sideband). The new frequency is converted back to the standard of rest of the source, and the resulting value is returned as the attribute value, in units of GHz.

Type:
Floating point, read-only.
Class Applicability:
DSBSpecFrame
All DSBSpecFrames have this attribute.


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AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 210
R.F. Warren-Smith & D.S. Berry
24th May 2011
E-mail:ussc@star.rl.ac.uk

Copyright (C) 2009 Science \& Technology Facilities Council