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Astron. Astrophys. Suppl. Ser. 141, 533-544

Transient correction of the LW-ISOCAM data for low contrasted illumination

A. Coulais - A. Abergel

Send offprint request: A. Coulais

Institut d'Astrophysique Spatiale, Bâtiment 121, Université Paris XI, 91405 Orsay Cedex, France

Received May 25; accepted September 15, 1999


The detector of the Long Wavelength channel of the ISOCAM camera on-board the Infrared Space Observatory (ISO) presents systematic memory effects of the response which can bias the photometry by a factor as high as 40$\%$. We show that, for uniform illumination, the non linear model developed by Fouks and Schubert (1995) for the detector of PHT-S channel of the ISOPHOT instrument allows us to describe the LW-ISOCAM response to upward and downward steps of flux with an accuracy better than 1$\%$. For each pixel of the detector, only two parameters have to be used. These parameters are constant over the whole life of ISO. On the other hand, spatial variations from pixel to pixel are significant.

We present an inversion method of the Fouks-Schubert model. Without any fitting and for low contrasted illumination, data are corrected with a photometric accuracy of $\sim $ 1$\%$, which is typically ten times better than previous methods. We suggest that the same approach could be used for others ISO detectors, and in the future for other experiments.

Key words: instrumentation: detectors -- methods: data analysis -- methods: numerical

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