Observing

Choosing Slit Width and Detector Binning

The slit width sets the approximate spectral resolution and should be chosen based on the science goal, seeing, and required signal-to-noise ratio. The detector binning should normally be chosen to match the slit width and seeing. The recommended values below are given as BINSPAT x BINSPEC, i.e. spatial binning by spectral binning.

Table 1: Recommended NGPS detector binning configurations. Entries are given as BINSPAT x BINSPEC, i.e. spatial binning by spectral binning.

Seeing (FWHM) 0.5” slit 1.0” slit 1.5” slit 2.0” slit 1.0” 2x1 2x2 2x3 2x4 1.5” 2x1 2x2 2x3 2x4 >2.0” 4x1 4x2 4x3 4x4

For most observations, spatial binning of 2 is adequate. Use spatial binning of 4 mainly in poor seeing. Spectral binning should usually scale with slit width: 1 for a 0.5” slit, 2 for a 1.0” slit, 3 for a 1.5” slit, and 4 for a 2.0” slit.