Observing Strategies For Strong Continuum Sources

Spectral line observations of strong continuum sources leads to a great amount of structure (i.e. ripples) in the observed spectra. So observations of strong continuum sources requires careful consideration of the observing setup and the techniques used.

If you are trying to observe weak broad spectral lines (wider than ~100 MHz) toward a source with strong continuum emission (more than 1/10th the system temperature), then you should consider using double position switching. This technique is discussed in an Arecibo memo [Ghosh and Salter, 2002].

Another issue is finding a proper IF balance that allows both the “on” and “off” source positions to remain in the linear range of the backend being used. This means that one must find the IF balance in both the “on” and “off” position and then split the difference - assuming that the difference in power levels between the “on” and “off” do not exceed the dynamic range of the backend. The BalanceOnOff() procedure in AstrID can be used to accomplish this type of balancing.