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SOFI User’s Manual - 2.0
Parameter signature
Exposure Name
DIT
NDIT
Number of columns
Number of rows
First column of window
First row of window
NJITT
NEXPO
Jitter Box Width (arcsec)
Filter wheel 1
Filter wheel 2
Instrument Mode
Combined Offset? (T/F)
Return to Origin? (T/F)
RA Offset List (arcsec)
DEC Offset List (arcsec)
LSO-MAN-ESO-40100-0004
21
Value
SOFI Map
10
6
1024
1024
1
1
6
9
40
Ks
open
LARGE FIELD IMAGING
F
T
0 450 450 0 -450 -450 0 450 450
0 0 0 -450 0 0 -450 0 0
Table 3.3: Parameters of the SOFI img obs AutoJitterArray template with commonly used values.
SOFI img obs AutoJitterArray 1 as the area mapping.
There are two distinct cases:
(i) Observations of “semi-extended” objects as large of a quarter to half of the SofI filed of view; these
may be moderately distant galaxies, small Milky Way clusters or LMC/SMC clusters. They are too
big for simple jittering mode observations but still leave room for more efficient observing strategy
where the observer does not need to sample clear sky 50% of the observing time. Instead, the user
can observe the sky simultaneously with the target, adopting clever offsets that would move the in
the centers of the four quadrants, or two halfs of the array. In the latter case, a suitable rotation
offset may be necessary to align the side of the array with the major axis of the object.
A typical example of a 4-point observation is shown in Figure 3.1. The figure shows the target –
a round object with diameter 90 arcsec – as it will appear on the RTD and on the SofI images.
The best choice is to use the template SOFI img obs AutoJitterArray 1. As it is described in
Section 3.2.4 this template allows the user to take a sequence of jittered images around user-defined
positions: first, all positions are imaged ones, then a random jitter is added to the entire pattern and
it is repeated as many times as necessary. Note that the offsets are executed before the images are
taken, and the offsets are defined along RA and DEC, in arcseconds. On the figure, the images in
the sequence are numbered to show the order in which the target will move during the observations.
The zero number is the location of the target acquisition and it will be discussed further.
The parameters of both templates are listed in Table 3.4. Note that for 4-point observation the
NEXPO parameter must be equal to four! Therefore, the total integration per position is controlled
by the time spent per on each image (= DIT×NDIT, usually 1-3 minutes) and by the number of
jittered images taken at each individual position NJITT. In this example, the total integration time
is: NJIT×NEXP×NDIT×DIT = 12×4×10×6=2880 sec.
In general, the template allows to define manually the offsets for each individual image. However,
this is inconvenient if the number of images is large. To simplify the matter, we suggest to the user
to define a “closed” loop, where after four images the telescope points back to the original position.
This means that the sum of the offsets along the RA is zero, same as the sum of the offsets along the