Konkoly Observatory, Budapest, Hungary
20 December 2006
The authors present 64 ISOPHOT observations of 64 extragalactic objects. They were observed in sparse map mode with the C100 detector after revolution 95.
The data set consists on:
A detailed report is available
List of caveats applicable to PHT observations performed with detectors C100 and C200 corrected in this work:
As described in the data processing report a flux dependent transient correction on all C100 data using an IDL routine is applied. For details of the algorithm see del Burgo et al. (ESA SP-511, 2002). The correction noticeably improved the results at intermediate fluxes (~ 2-16 Jy).
Formal flux uncertainty values were provided by the IDL procedure which fitted the measured fluxes of the different pixels as a function of the footprint values (see data processing report). The range of resulting flux errors is consistent with a robust standard deviation of the measured galaxy fluxes around a mean value close to zero, verifying that the flux uncertainty values provided by the fitting routine are reasonable.
The ISOPHOT-C detectors show a non-linear response with flux. The established linearity correction is only valid for certain ranges, covered by calibration standards. For a compilation of these signal ranges, for each filter, please refer to PHT Handbook Section 10.10. The polynomial approximations to the non-linearity curves are not extrapolated beyond the calibrated signal range, but are kept at the level of the boundary. This may introduce some unsteadiness in corrected signals, including those for different filters. As mentioned in the data processing report, our tests on normal star observations performed in sparse map mode show no obvious systematic photometric discrepancies as a function of stellar flux, indicating that the restrictions in the signal non-linearity correction do not lead to noticable quality decrease inthe present sprase map data set.
The flux extraction method adopted in our data reduction scheme is based on a simultaneous fitting of the background level and the source flux using the point-spread function, and is not affected by this caveat
All observations of the present data set were observed after revolution 94.
In our processing the flux was reconstructed with the help of the detector footprint shape.
As described in the data processing report in those cases when enough data points were available the long term drift evolution was fitted with a low order polynomial and subtracted from the observation. Also, the introduction of time dependent flatfield arrays contributed to the cancellation of the responsivity drifts.
The flux extraction method adopted in our data reduction scheme is based on a simultaneous fitting of the background level and the source flux using the point-spread function.