The principal investigator for ISO PHOTometer is D. Lemke (MPIA, Heidelberg, Germany). ISOPHOT comprises 3 sub-systems, a photometer which can do polarimetry at short wavelengths in addition to multi-aperture, multi-filter photometry (PHT-P), a long-wavelength, photometric camera (PHT-C), and two low-resolution, grating spectrophotometers (PHT-S). PHT-P covers the wavelength range 2.5um to 120um with 14 filters (resolving power ranges from 1.7 to 17.4). The 13 apertures vary in diameter from 5.0" to 180" (although 2 of them are rectangular not circular). Polarimetry is possible with PHT-P between 2.5um and 30um. PHT-C has 2 two-dimensional mosaic arrays of detectors, operating from 50um to 200um. There are 6 filters for the shorter wavelength camera array (which has nine 43.5" pixels), and there are 5 filters for the longer wavelength camera (which has four 89.4" pixels). Polarisation can be done with any filter in PHT-C. The two grating spectrophotometers in PHT-S operate from 2.5um to 5um and from 6um to 12um. Each spectrometer has an array of 64 detectors, and PHT-S has a resolving power of around 90.
PHOTOMETRY: There is a wide range of photometric observations possible, using PHT, including multi-filter, multi-aperture, absolute photometry (w.r.t. internal calibrators), and these may be made with single pointings, raster scans, linear scans, variability monitoring or sparse maps. Chopped observations can be made with background up to 330" away (depending upon the selected aperture). The aperture given here is the diffraction limited one. Only point source sensitivities are given here. The sensitivities are estimated using an intergration time (on source) of 100 sec, and S/N=10, assuming moderate background.
Filter Resolving Aper. Flux Comments power limit PHT-P P_3.29 17.4 5.0 31mJy Feature P_3.6 3.4 5.0 6.2 Common to SWS P_4.85 3.2 7.6 4.2 P_7.3 2.3 13.8 2.6 P_7.7 9.8 13.8 12 Feature P_10 5.6 18 7.9 P_11.3 15 18 29 Feature P_11.5 1.8 23 2.5 IRAS-like P_12.8 5.6 23 6.7 P_16 4 23 6.5 P_20 2.3 52 7.7 P_25 2.6 52 8.5 IRAS-like P_60 1.7 99 35 IRAS-like P_100 2.3 180 91 IRAS-like PHT-C C_50 1.3 45 C_60 1.7 43 C_70 1.8 35 C_90 1.7 20 C_100 2.3 33 C_105 2.8 57 C_120 2.3 31 C_135 2.2 28 C_160 2.0 25 C_180 3.1 56 C_200 5.7 258 Aperture list Size (arcsec) Comments 5.0 circular 7.6 circular 10 circular 13.8 circular 18 circular 20 x 32 Common to SWS 23 circular 52 circular 79 circular 99 circular Common to LWS 120 circular 127 x 127 180 circularPOLARIMETRY: The 3 polarisers + clear aperture can be viewed by both PHT-P (not with the 60um and 100um filters) and PHT-C. The sensitivities are calculated with an exposure time of 100 sec for each polariser setting, and a required absolute error in the degree of polarisation of 1%. A polariser illuminated with unpolarised radiation transmits a fraction T of the incident intensity. P' is the degree of polarisation of the transmitted radiation. Each polariser is used twice in an observation, to improve reliability. Observations are permitted through one filter, several filters, several apertures, with the possibility of a raster scan or sparse map. Only point source sensitivities are given here.
Filter Central Polariser Eff Flux wavelength T P' limit PHT-P P_3.29 3.30 0.35 0.90 656mJy P_3.6 3.63 0.35 0.90 160 P_4.85 4.85 0.35 0.91 108 P_7.3 7.4 0.35 0.91 64 P_7.7 7.65 0.35 0.91 307 P_10 9.90 0.35 0.92 194 P_11.3 11.4 0.35 0.92 720 P_11.5 11.8 0.35 0.92 51 P_12.8 12.8 0.35 0.93 160 P_16 15.6 0.35 0.94 152 P_20 20.7 0.35 0.96 147 P_25 23.9 0.35 0.97 170 PHT-C C_50 66 0.52 0.89 757 C_60 64 0.51 0.92 717 C_70 80 0.50 0.95 579 C_90 93 0.50 0.96 311 C_100 100 0.50 0.97 534 C_105 105 0.50 0.97 925 C_120 115 0.51 0.98 468 C_135 146 0.51 0.99 419 C_160 160 0.52 0.99 362 C_180 173 0.52 0.99 850 C_200 188 0.52 0.99 3990