To evaluate aperture-to-aperture differences, we proceeded to evaluate shifts from cross-correlations of similar spectra. We chose NEWSIPS-processed spectra from several well observed OB and white dwarf stars. Table 1 gives the numbers of IUE high-dispersion echellograms used for the analysis of the SWP camera data. As before, these data were cross-correlated for echelle orders m = 70-119. The zero-point errors are expressed in velocity units, a represention that we justify in 4.1.. Table 1 shows that both the mean differences, expressed as RVLGAP - RVSMAP velocities, are -0.8 km s-1 for six bright stars and -0.7 km s-1 for six white dwarfs. The mean shift for any one of these stars is accurate to about ± 2 km s-1 or better. Thus, there are no noticeable systematic differences for shifts between the two apertures and between the over-/underlap modes guiding modes.
|Bright Stars:||10 Lac||Sco||Oph||UMa||Lep||Cas|
|LGAP - SMAP||0.4||-3.5||-0.6||+0.2||+0.2||-1.7|
|Faint Stars:||RR Tel||Sirius B||BD+75o325||BD+28o4211||HD93521||HD60753|
|LGAP - SMAP:||-2.5||-2.3||-4.7||2.4||2.1||0.7|
|LGAP - SMAP||-2.5||-1.1||0.1|
|LWR Camera:||10 Lac||Sco||Oph||RR Tel|
|LGAP - SMAP||1.9||-1.0||-4.3||+4.3|
Table 1 lists similar results for three stars for the LWP camera and four stars for the LWR. The mean LGAP - SMAP difference for the two cameras are -1.2 ± 3 and +0.2 ± 3 km s-1, respectively. The quoted errors are sums (added in quadrature) of both LGAP - SMAP differences and zero-points of individual SMAP observations. From this work it is clear that no major systematic aperture-to-aperture differences are detectable for any of the three cameras.