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For all observations performed after the resumption of LWS observations (31 January 1997), the LWS processing does not produce Auto Analysis results (AAR) for AOTs L01 and L02. The reason for this is that the way the internal calibrators are operated has changed (it used to be with FPS in the beam, now it is with FPL). The processing software currently used does not account for the changed calibration configuration, and therefore cannot create an AAR (the internal calibrators are used in Auto Analysis for the responsivity correction and the flux calibration).
For the FP observations the situation is different, because here the FP that is used for the scientific observation, is also used for the calibration.
NOTE:
In a few cases, ERD and SPD products have been send out by accident for L01
and L02 observations. Observers are advised that these observations have
been performed correctly and the ERD and SPD files are correct. However,
no AAR could be generated for the reson stated above. All these LWS data
will be reprocessed with version 6.0 of the Off-line processing, starting
May 5 1997 and will be resent to the observers.
In the data products derived for the FPs, some data can be marked as bad, although there is in principle nothing wrong with this data in the SPD file. The reason for this discrepancy lies in the way the responsivity correction is performed for FP data. The processing software determines for each line where the FP is expected to be for the position of the grating that was used. This expected FP position depends on the order that the FP is working in. The software then checks that the FP was indeed scanned around this expected position. If this is the case, the responsivity correction is done for this grating and FP position. If the FP however was scanned around a value which is not expected by the data processing software, it currently flags the data as invalid. This is due to the fact that the calibration files used for deriving the products do not yet contain valid responsivity for a number of FP positions (especially at points where the order of the FP, which is used, changes).
The new calibration files which will be used for Version 6 of the Off-line processing will solve most of the problems with the order selection. All L04 data will be reprocessed through version 6 of the Off-line processing software starting May 5 1997, and will be resent to observers.
The data taken with the L03 AOT will process correctly through version 6 of the LWS processing software (starting 5 May 1997). However the data products should only be used for identifacation of lines, since the flux calibration (and especially the responsivity calibration) can be significantly off for this AOT. An automatic processing system that derives an accurate flux calibration for this AOT is unlikely to become available. However, the LWS Instrument Team plans to use the Guaranteed Time data on the Galactic Centre to investigate if any software (IDL) tools can be written to correctly process these data manually.
For the moment the data may show strange spectral shapes, and even negative fluxes due to the dark current removal and flux calibration problems.
ISO Science Operations
09/04/97