3.2 Single-Pointing Multi-Filter and Multi-Aperture Modes

With single-pointing photometry it was possible to measure the energy distribution of point-like or compact extended sources in broad-band filters. For the detection of dust features dedicated narrow band filters were available, and there were some very broad filters dedicated to the detection of faint sources. Figures 3.2, 3.3 and 3.4 give some typical combinations of filters for different scientific purposes, and the complete set of ISOPHOT bandpasses is displayed in Appendix A.2.

Figure 3.2: Relative system response (i.e. detector response normalised to its maximum value) of PHT filter bandpasses: near and mid infrared PHT-P filter sequence 3.6 - 25 m (left); and the corresponding IRAS filter sequence with PHT-P (right)

Figure 3.3: PHT filter bandpasses: combination 1 of far infrared PHT-C filters (left); and combination 2 of far infrared PHT-C filters (right)

Figure 3.4: PHT filter bandpasses: the very broad band filters for low flux detections.

The large set of apertures in the PHT-P subinstrument offered the study of faint extended emission around point sources, by means of multi-aperture photometry. The largest apertures permitted detection of faint and extended emission, either in staring or chopped mode. For the chopped mode the restrictions in chopper throw described in Section  3.1 had to be applied to the largest selected aperture.