Setting Up Pointing Scans and Tipping Scans

by Gustaaf Van Moorsel last modified Jan 17, 2018 by Lorant Sjouwerman

Pointing scans are typically done at X band (8 GHz) on strong (> 0.3 Jy/beam) continuum sources near your target source, i.e., within about 20 degrees. Most likely you will find such a source in the VLA calibrator catalog. Note that for longer tracks, the optimum pointing source is at roughly the same Declination and about 10 degrees earlier in LST (40/cos(Dec) minutes in RA), but the source itself (if bright enough in X band) is also a relatively safe bet. You may want to add the pointing source to your personal source catalog if it is not in there already. If you plan on doing secondary reference pointing scans (see the next chapter) and your intended pointing source is not strong enough at the observing frequency you wish to use for the secondary reference pointing scan, you may need to add another pointing source that is strong enough at this frequency, or perhaps even revisit your first choice. More details can be found in the Observing Guide.

Tipping scans on the other hand are typically done independently of your sources. The only interest is the observing frequency and the direction, in Azimuth, of the main distribution of your sources so that the opacity is measured in the global direction of your targets and the slew time between sources and tips is minimal. Tipping scans currently are set up in the OPT only; no extra sources are needed.