Spectral Line Resources

There is no separate example of a spectral line resource in the NRAO defaults catalog. The WIDAR correlator writes all its data in spectral line form, meaning that the continuum resources described above are already spectral line resources. However, when the scientific interest is in a specific line, typically one would want to use a spectral resolution that is better than the spectral resolution in the continuum resources above. The correlator would be set up to provide data with narrower frequency channels than 2 MHz, tuned to the line frequency when corrected for (approximate) Doppler shift. Currently, during the OSRO period, there are two possibilities to do this, depending on the requirements on polarization and width of the frequency channels:

  • For polarization measurements all polarization products are needed. The correlator must be configured as OSRO1, centered at the anticipated observing frequency. The total number of frequency channels is 128 (twice 64), and the frequency channel bandwidth can be selected to be from 2.0 MHz, in steps halving the width, down to 488 Hz. The total bandwidth will be twice 64 times the channel width.
  • If total intensity (Stokes I) is sufficient, the correlator may be configured as OSRO2, centered at the anticipated observing frequency. The total number of frequency channels is now 256, and the frequency channel bandwidth can be selected to be from 0.5 MHz, in steps halving the width, down to 122 Hz. The total bandwidth will be 256 times the channel width.

The difference in correlator configuration between OSRO1 and OSRO2 is that giving up one output pair and giving up the cross polarization products from OSRO1 each doubles the frequency channels available in OSRO2. However, if the science requires the simultaneous observation of two lines separated by more than the total bandwidth of the single output pair, the observations must be done using OSRO1 and the trade-off is using less channels per line or using a coarser spectral resolution. For example, simultaneously observing the SiO lines at 42.8 and 43.1 GHz would require OSRO1, the continuum resource2.2.

Note that at the moment Doppler calculations using a rest frequency is disabled. Check section A.3 for more information.

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