Keywords: map

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### How to optimize single-dish observations?

One of the main difficulty of the short-spacing problematic is the need of observations from a single-dish telescope different from the interferometer. In this respect, the IRAM-30m and PdBI are very complementary. Nevertheless, when observing with the single-dish telescope, a few precautions are needed to avoid contaminating the interferometric data with possible artifacts of single-dish data.

- The field-of-view of the single-dish map must be twice the field-of-view covered by the mosaic. The only exception to this rule happens when the source intensity decreases to zero in a smaller field-of-view. Indeed, there is no point in observing an empty sky.
- The observing strategy must enforce Nyquist sampling (or better) of the source at the resolution of the single-dish telescope.
- A particular care should be taken of the pointing, tracking and amplitude calibration and baseline removal as those are critical issues in obtaining a high quality single-dish map to produce short-spacing information. For instance, data with too large tracking errors should be discarded.
- We advise to make many On-The-Fly coverages of the observed field-of-view to get homogeneous observing conditions. Scanning in perpendicular directions is needed to decrease stripping.

Sometimes, single-dish telescope time is scarce and some of the above criteria can not be fulfilled. In those cases, you can still try to use your single-dish observations and our algorithm will try to make its best to get a sensible result. However, any artifact in the combination may directly come from wrong single-dish observations. In other words, do not blame the software unless you are sure of the quality of the quality of your single-dish (and interferometric) observations...

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