The FUSE Archival Data Handbook - MAST - STScI

are constructed. It is thus recommended that users examine the count-rate plots (see Section
4.2.1.4) for the individual exposures before accepting the NVO file at face value.
Additionally, cross-correlation may fail, even for the spectra of bright objects, if they lack
strong, narrow spectral features. Examples are nearby white dwarfs with weak interstellar absorption
lines. If cross-correlation fails for a given exposure, that exposure is excluded from the
sum. Thus, the exposure time for a particular segment in an NVO file may be less than the
total exposure time actually available for a given observation.
NVO data files contain columns with WAVE, FLUX, and ERROR stored in a single binary
table extension (see Table 4.15). Figure 4.9 shows the NVO spectrum of observation D0640301
for target HD91597, with corresponding filename: D064030100000nvo4ttagfcal.fit.
Figure 4.9: Plot of an exposure-summed spectrum (black trace) and its associated error array
(red trace) for observation D0640301 (*nvo.fit). The error array contains sharp discontinuities
due to the fact that the data from different segments have been spliced together to form this
overview spectrum.
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