The conceptual design of the instrument is driven by the WEAVE science
requirements, as defined by the Science Team, and translated to technical
requirements by the Project and Instrument Scientists. At the
time of writing the requirements call for a dual-beam spectrograph with
the following characteristics:
| Specification |
Requirement
|
Goal |
| Field of view diameter |
2 degrees |
2 degrees |
| MOS multiplex |
800 |
1000 |
| Atmospheric dispersion
compensation |
0.4-1.0 µm,
50oZD |
0.37-1.0 µm, 60oZD |
| MOS fibre aperture |
>=1.2" |
1.5" |
| Open shutter efficiency
(1 hour observations) |
70% |
90% |
| Wavelength coverage |
400-950nm |
370-1000nm |
| Spectral
resolution (full simultaneous coverage) |
5000 |
5000 |
| Spectral
resolution (reduced coverage) |
20000 |
20000 |
| Stray light as function
of faintest target |
<1% |
|
| Blue system efficiency |
20% |
25% |
| Red system efficiency |
25% |
30% |
| Multi-IFU multiplex |
10 |
30 |
| Multi-IFU FOV |
9" x 9" |
9" x 12" |
| Multi-IFU spaxel size |
0.8" |
>1.2" |
| Single IFU FOV |
3' x 3' |
|
| Single IFU spaxel size |
2.5" |
Inner 1", outer 2.5" |
The philosophy behind the construction of WEAVE is to keep it simple
but effective. Thus the design exploits the use of COTS (Commercial
Off-The Shelf) components which not only reduces project costs and risks but
provides an attractive solution for maintaining the instrument throughout its
lifecycle.
The Positioner
Pick-and-place technology will be used to position the fibre buttons onto a
plate using a commercially available X-Y gantry. A computer simulation
shows the complexity of weaving 920 fibres to acquire their targets.
Each green line represents a single fibre and the purple beads are the magnetic
buttons. In this particular example there are 8300 fibre crossings. |
At the edge of the field are the fibre retractors (originally designed for GYES)
that tension and protect the individual fibres. Each retractor holds four
fibres and the buttons are seated at the entrance to the retractors as
illustrated in the following pictures.
|
Actual retractor designed and built for GYES. |
The fibre positioning mechanism is a twin-based system of fibres, retractors and
buttons etc. The arrangement is s uch that 1000 fibre-assemblies are
positioned at each end of the rotating assembly also known as the tumbler.
This fits inside a gantry with a robotic gripper that places the buttons on the
plate. This arrangement allows for reconfiguration of the top plate whilst
the bottom plate is used for observing.
|
The Spectrograph
Fibres from the positioner are fed to the dual-beam spectrograph which
incorporates a dichroic at ~600nm and has two volume phase holographic gratings.
The spectrograph will be housed in GHRIL.
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