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VIMOS User Manual
VLT-MAN-ESO-14610-3509
Table 2.7: Spectral coverage ∆λ for three positions of the slit in field of view (MOS mode)
Grism
LR red
LR blue
MR
HR blueN EW
HR blueOLD 2
HR red
HR orange
Order sorting
filter
OS-red
OS-blue
GG475
Free
Free
GG475
GG435
∆λ
CCD center
550 - 950 nm
360 - 670 nm
500 - 1000 nm
370 - 535 nm1
370 - 552 nm
630 - 870 nm
520 - 760 nm
∆λ
CCD bottom
550 - 950 nm
360 - 670 nm
500 - 1000 nm
370 - 624 nm1
468 - 674 nm
690 - 930 nm
577 - 817 nm
∆λ
CCD top
550 - 950 nm
360 - 670 nm
500 - 950 nm
370 - 451 nm1
370 - 566 nm
570 - 805 nm
463 - 703 nm
1
HR blueN EW The ranges correspond to Q1 for slits positioned at y=50, 1220, and 2390 in the acquisition
image for the bottom, center, and top ranges, and it is common to all quadrants. For other quadrants visit the
VIMOS web pages.
2 HR blueOLD not available after March 2012. Info given for reference.
for a total of 6400 fibers.
2.4.1
IFU mode: orientation of the field of view
Figure 2.5 shows the orientation of the instrument field of view in IFU mode for the four quadrants. On the
detectors, wavelength dispersion is along the y axis, with wavelength increasing with y. An actual example
for PA=0◦ is shown in Fig. 2.6. The increasing position angle on the sky (east of north) corresponds to the
positive rotator angle. Spatial characteristics are described in the Section below.
As for IMG/MOS modes, the pointing coordinates in the header correspond to the center of the VIMOS
field of view. Due to the offset position of IFU with respect to the center, the keywords RA and DEC in
the headers do not refer to the IFU pointing, but rather to the center of the VIMOS FoV. Prior to P91 the
only way to determine the actual position of the IFU was using the center coordinates, together with the IFU
offset position, coded in the keywords ”HIERARCH ESO OCS CON WCS IFUCENX”, and ”HIERARCH
ESO OCS CON WCS IFUCENY”, and the PA on sky (after some spherical trigonometry). This was needed
because the only other relevant information on the headers was ”HIERARCH ESO TEL TARG ALPHA”, and
”HIERARCH ESO TEL TARG DELTA”, which contained the coordinates of the target. Any offsets from the
original pointing would result in an IFU pointing that would differ from these keywords. Starting in P91 the
relevant header keywords which contain the information of the actual pointing of the IFU are ”HIERARCH
ESO INS IFU RA” and ”HIERARCH ESO INS IFU DEC”. Notice that the whole ESO archive of IFU data
has been retro-fitted with these keywords, so now it is possible to search for IFU observations simply queryng
by target coordinates.
2.4.2
Fiber arrangement and spatial characteristics
The special arrangement of fibers for VIMOS IFU head is shown in Fig. 2.7. The fibers numbering has been
arranged following the scheme: mask - line - module -fiber (i.e. 4 - B - 5 - 67). The arrangement of the fibers
into the 4 pseudo-slits mask (one for each channel) is reported in Fig. 2.8. The detailed IFU table is distributed
to the users together with the data release.
A masking-shutter (IFU shutter) is provided in front of the input micro-lens array; this allows the exclusive
use of the central 1/4th of the field when IFU is used with intermediate and high spectral resolution grisms. In
this configuration, only 1 fiber-slit per quadrant (mask) is used, for a total of 1600 fibers. The templates for
IFU mode offer the option to insert a shutter to limit the field to the central part also for low resolution grisms.
When small field can be accommodated, this avoids second order contamination by the sky or background