PHT-P

This subsystem is designed for sensitive, high precision photometry and polarimetry, using three different single detectors, where only one can be used at a time (in parenthesis the detector material is given).

• P1 (Si:Ga) 10 filters: 3.3 - 16 m
• P2 (Si:B) 2 filters: 20 and 25 m
• P3 (Ge:Ga) 2 filters: 60 and 100 m

Any combination of polarisers, apertures and filters is allowed. At long wavelengths the Airy disc is significantly larger than the smallest aperture available. The diameter of the Airy disc is =0.84m]. The selection of apertures much smaller than is not recommended (cf. Tab 1).

 

Polarisers: 0, 120 and 240 degrees
Apertures: 5.0, 7.6, 10, 13.8, 18, 20x32, 23, 52, 79, 99, 120, 127x127 and 180. All apertures are circular except as noted.

The precision of the ISO pointing has implications on the achieved photometric accuracy. When observing with the smallest PHT-P apertures (5.0, 7.6, 10, and 13.8), the source may be off-centre or even outside the aperture. See ISO Observer's Manual for details about the ISO pointing accuracy.