ISOPHOT C200 chopped observations (I)
Peter Ábrahám, Csaba Kiss
Konkoly Observatory, Budapest, Hungary
The authors present a full catalogue of 605 ISOPHOT observations
(1228 measurements) of 542 compact objects. They were observed in chopped mode with the
C200 detectors after revolution 95. The catalogue is split into two separated catalogues.
First one contains observations which use only the C200 detector array. They are 206
ISOPHOT observations of 189 compact objects. This catalogue (I) is the "default dataset"
in IDA for these 206 observations.
The data set consists on:
The final photometric values are presented in the
form of a catalogue that can be queried from the
AAP data structure files as produced by PIA 10.0
and the same in FITS format.
ISO Data Archive.
A detailed report is available
List of caveats related to C200 chopped observations corrected
in this work:
CAVEATs for DETECTORS C100 & C200:
Restricted signal non-linearity correction
As part of the processing scheme of the C200 chopped mode, signal linearity was
tested and corrected via applying a correction factor dependent on the flux
level. In addition, we determined non-linear transformations between the
measured signals of different pairs of C200 pixels, and used these formulae
in order to transfer all four pixels's signal into the photometric system of
Pix. 3. As a last step of the processing scheme an empirical flux-dependent
correction was 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.
Aperture correction factor for point source applied!
The adopted flux extraction method - fitting the measured point source function
to the observed flux distribution rather than summing up all fluxes on the array
and correcting it for losses outside the array area - ensures correct
FCS calibration quality restricted
All measurements included in the catalogue were observed after Rev. 93.
Aperture photometry from surface brightness maps
For flux extraction we always use PSF-fitting
(the flux was reconstructed with the help of the detector footprint shape)
rather than aperture photometry.
In chopped mode 1-2 background positions are always measured.
In the HPDP catalogue we present non-colour corrected fluxes. Proper
colour correction requires knowledge on the SED of the object, and is thought to
be the responsibility of the user.
General caveats applicable to all PHT observations:
Signal losses due to detector transients - which can be dramatic in the case
of the C100 detector - are at the 10-20% level for the C200 camera. Since the
signal loss depends on the flux level, our flux-dependent empirical photometric
correction is expected to correct for it to a large extent.
Incomplete Error Propagation
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 group of measurements having independent
flux prediction ('secondary standards') are also assessed by computing the
standard deviation of the [measured - predicted] flux differences.
The final formal uncertainties were determined by combining the two types of
error bars. As usual in the case of C200 measurements the dominant factor of
the measurement uncertainty is the sky confusion noise.