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As discussed during the second
data analysis workshop, IRS observers using the SL1 (Short-Low, first
order) module may notice excess emission between 13.2 and 15 microns in
their S13 pipeline-processed data. We refer to this feature as the "14
micron teardrop", and it is shown in Figure 1.
While this excess was present in previous pipeline-processed data, it is
only the improved quality of the calibration for S13 that has allowed us
to isolate this feature and removed this wavelength region from our fits
to the calibrator spectra. We believe that the teardrop is a type of
scattered light, but it's origins are not well understood, and are
currently under investigation. The amplitude of the excess varies with
the source strength and the extraction aperture, since the teardrop is
resolved spatially. The difference between the S12 and S13 processing for
a point source extraction can be ~10% as shown in Figure 2. For a point source, the flux ratio between
the default point source extraction width (8 pixels at 12 microns) and
full slit extraction shows an excess of up to 15%, longward of 13 microns,
compared to the ratios at adjacent shorter wavelengths. We strongly
caution the users against interpreting any broad features longwards of
13.2 microns in SL1.
Figure 1
Figure 2
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