ISO Explanatory Library : SWS

ISO Explanatory Library: SWS

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Next: Bibliography Up: olp101sws Previous: 4. Choice of Models

5. Verification of the New Calibration

In figure 5 we show a rebinned aar with the new calibration divided by the OLP10 AAR. This can be compared to the mean ratio curve of the STARTYPE group (figure 1). We see a qualitative agreement in the differences around 4.5 $\mu$m and the difference in the short-wavelength end of 2C. We interpret the 2% features in the 9-12 $\mu$m region in the curve in Figure 1 as noise in the residues due to large differences in memory effects.

During the scientific validation of OLP 10.0, L. Decin described two wavelength regions where the RSRF correction could be improved in band 2A and 2C. The features she described in the comparison of synthetic spectra and OLP10 SWS spectra compare well with the changes to the RSRF calibration for OLP10.1.

We believe the accuracy of the absolute and relative flux calibration has improved with the new delivery. The improvement, however, is at a level smaller than the typical reliability of individual band 2 observations because of memory effects. An example can be seen in Figure 6. We have plotted an AOT1 and an AOT6 observation of sirius, processed with OLP 10 and the new calibration. One can see that the difference between the two observations (with different scanning strategies and hence different memory effect regimes) are comparable to the differences between the two calibrations (we only consider the short wavelengths, at longer wavelengths the situation only gets worse).

Figure 5: The division of a rebinned OLP10 AAR and an AAR processed with the new calibration.
\resizebox {12cm}{!}{\includegraphics{diff_olp10_cal060.ps}}

Figure 6: Two observations of Sirius : AOT1 (black) and AOT6 (green) as processed with OLP10. The blue and the red curves show the same data processed with the new calibration used in OLP10.1.
\resizebox {12cm}{!}{\includegraphics{sirius_olp10_olp11.ps}}

We should be aware of the fact that, although we might have taken away concerns about biasing to errors in synthetic spectra, there is a risk that the (1) low number of observations, (2) the similarity of the spectral shape in the observations and (3) the nearly identical observation mode (AOT1 speed4, Vega is observed with speed 3) in the new calibration can introduce a systematic bias to the typical memory effect signature in AOT1-speed 4 observations of hot stars. We have verified that this bias is in any case not worse than the bias previously present in the olp 10 calibration.

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Next: Bibliography Up: olp101sws Previous: 4. Choice of Models
Improvements in the OLP 10 RSRF and Flux Calibration of ISO-SWS Bands 2A and 2C