User Manual
Doc. Number: ESO-323064
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the foot
print of the 0.4” slit vignettes an area of 0.4”x10” about 8” Eastward with respect to
the slit centre (see dark vertical strip in Figure 25).
Figure 25: Geometry of the SV detector for PA of 0 deg on sky. North is up and East on the
left. The un-
vignetted FoV usable for target acquisition and guiding is ~22.8” x 30.8”. The
centre of the usable FoV and of the slit is
marked as white cross. The slit centre (0.2” in this
example) does not match the un-
vignetted FoV centre, but it’s displaced by 3.6” W and 0.2”
N. When using the 0.2” slit, the footprint of the 0.4” slit vignettes an area of 0.4”x10” located
~3.6” Eastwards with respect to the FoV centre (see vertical dark stripe). When the 0.4” slit
is used, there is no vignetting from the 0.2” slit as it
s footprint falls at the border of the FoV.
4.4.2 Slit viewer limiting magnitude
The SV is equipped with 5 NIR filters: J, H, K and 2 neutral density H filters.
The SV is sufficiently sensitive that any emitting point source for which one aims to obtain
a spectrum should be seen on the SV image. In particular, in AO mode, stars of H
~
15 are
easily detected in a 10 s exposure, a typical time scale for guiding
.
In NoAO mode, H~15.5
stars are barely detected (3
) in a similar 10s integration under 0.9
”
seeing when located
away from the slit.
For guiding on target (TRG=SVGS), the limiting magnitude is much brighter as only a small
fraction of the light is reflected by the slit jaws to the slit viewer detector. During the on-sky