The ISO Camera (ISOCAM)

PI: C.J. Cesarsky, Saclay, F

ISOCAM will provide imaging capabilities in the spectral region from 2.5 to 17 m across a field-of-view (f.o.v.) up to 3 arcmin in diameter at various spectral and spatial resolutions. The instrument consists of a short wavelength channel (SW) and a long wavelength channel (LW). One optical channel is used at a time. Both channels have sets of filters, including Circular Variable Filters (CVF) for spectrophotometric work, that can be placed in the light beam. The spectral resolution in both channels is about 40 for the CVF's and ranges from 2 to 30 for the band pass filters. The detectors are 32 32 pixel arrays. The observer can choose a pixel field-of-view (p.f.o.v.) of 1.5, 3, 6 or 12 arcsec. However the spatial resolution is limited by diffraction and by the pointing of the satellite.

ISOCAM will perform imaging in one of the two channels using one or more p.f.o.v. and one or more filters or CVF positions. A celestial raster may also be performed allowing larger areas than the camera f.o.v. to be covered. In addition if the raster step is a few pixels only, the same part of the sky will be measured with a number of different pixels of the detector. As a result one of the most dominant noise terms, the flat field, can be much better determined. This micro-scanning mode is recommended for weak, confused or extended sources or in the presence of a structured background. There is also a beam switching mode, dedicated to photometry, recommended for weak isolated sources. The beam switching mode allows different reference fields within 1 degree of the source position to be observed enabling large scale gradients in the background to be removed. Spectrophotometric imaging can be performed with the CVF's, but this mode cannot be used with beam switching or raster mapping. Polarimetric imaging can be taken through three polarizers mounted at the entrance wheel, each 60 deg apart on the sky.

Recently the ISOCAM flight model has been integrated in the payload module. Tests at liquid helium temperature have been very successful. The health of the detectors and micro-processors have been checked and all wheels are operating. For the LW channel, tests demonstrate that the temperature regulation system works as expected and all signals measured confirm (within 3%) results obtained at the instrument test facility at Orsay. The SW detector reproduced previous results at Orsay within 5%. Different temperatures of the SW detectors during both runs may account for the difference.

The spare model of ISOCAM Focal Plane Unit was successfully vibrated at room temperature. After a number of functional tests, the calibration of the flight spare will be completed in the next weeks.

The ISOCAM performance simulator has been completed. It continues to be updated with the latest results provided by the Calibration Team.

As a summary, all present tests indicates that a highly sensitive mid-infrared camera is ready for launch into space soon.