Konkoly Observatory, Budapest, Hungary
19 June 2003
The authors present 555 ISOPHOT observations of 229 main-sequence stars (and additionally some giant stars from the ISOPHOT standard lists). They were observed in mini-map mode with the C100/C200 detectors after revolution 95. A few 1D-scans are also included.
The data set consists on:
Details of the data processing are described
List of caveats related to P22 mini-map observing mode 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). In the case of the C200 detector signal transients are small and negligible compared to other error sources (P. Héraudeau, private communication).
Individual error bars for each measurement are obtained as the standard deviation of flux values obtained by different detector pixels. In parallel the empirical total uncertainty for the whole ensemble of 555 normal star measurements are also assessed by computing the standard deviation of the [measured - predicted] flux differences. The two kinds of errors were in reasonable agreement. The results confirmed that the main components of the total uncertainty are instrumental noise and sky confusion noise. In the case of C200 measurements the dominant factor is the sky confusion noise.
As a last step of the processing scheme an empirical flux-dependent correction is performed which - signals and fluxes are approximately proportional - corrects to a large extent for the possible artifacts related to the restricted range of signal non-linearity correction (for all C100 & C200 filters but C70 the lower boundary of the signal linearization table was 0.0 and any artifacts are expected at very high fluxes).
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 2nd order polynomial and subtracted from the observation. This correction improved the photometric results significantly.
In a mini-map observation several raster steps observed the sky background. As part of the processing scheme the background level was computed and subtracted from the source measurement.