There are several potential anomalies that an investigator
should check in FUSE data:
- "Channel misalignments", which causes a drifting of the
the wavelength scale between pointings at different targets,
- Spectral astigmatism, which greatly reduces the ability to
differentiate spectra from two targets aligned along the "spatial"
direction of the science aperture),
- "X-walk", a slight spectral blurring induced by high voltage
in the detector,
- Air glow (emission lines from the Earth's atmosphere). These
during especially strong during solar maxima (2000-1)),
- "Event bursts", which produce patches of photoelectrons on
the detector.
Users should also be aware that fluxes of the LiF 1B spectral segment
observed through the LORES aperture are not well calibrated.
Line spread function studies demonstrate that narrow lines in
FUSE spectra have extended tails out to several pixels. For
closely spaced absorption lines (e.g., the Lyman series) this
can produce an anomalously high "background."
Users should always check the "trailer files" for anomalies in
processing the data for clues to unexpected pathologies in the
processed spectrum. They should also check the preview images
of the detector surface for unwanted signal.
A good discussion of these problems can be found in Ch. 2 of the
FUSE Observer's Guide.
