STUDY SUMMARY - IPMU

SUMMARY REPORT
WIDE FIELD FIBER-FED OPTICAL
MULTI-OBJECT SPECTROMETER (WFMOS)
Figure 2.3-1: Fractional precision of various surveys. Left panel illustrates the expected
fractional precision of various surveys in measuring the acoustic scale (using our own
S/N formula, as discussed in the OCDD). Right panel shows the fractional precision in
the growth rate (following White, Song & Percival 2008). The observed results for the
2dFGRS and SDSS at low redshift are plotted as points, together with the predicted
accuracy of the VIPERS VLT survey. The lines are intended to show the precision
expected in redshift shells of width 0.1. In the left-hand panel, we also show (triangle
points connected by dotted lines) the average precision expected from the full volume of
BOSS and of our WFMOS surveys......................................................................................... 11
Figure 2.4-1: A measure of the impressive data-gathering power of WFMOS in
comparison to other wide field spectroscopic facilities. The ordinate represents the
product of the multiplex and number of resolved spectral elements above a fixed
signal/noise per unit observing time. Our team has learned much from its extensive use
of the FLAMES and DEIMOS instruments, and this has been reflected in our WFMOS
requirements. .............................................................................................................................. 13
Figure 3.2-1: WFMOS Block Diagram ................................................................................... 19
Figure 3.6-1: Schematic of Single Camera on the Prime Focus Support Strut .............. 28
Figure 3.6-2: 1100 Series Camera from Spectral Instruments, Inc. ................................. 29
Figure 3.6-3: Optical Layout of the Subaru Telescope and the Metrology Camera....... 29
Figure 3.7-1: The WFMOS Field Element–to–Fiber Tip Coupling Efficiency .................. 30
Figure 3.8-1: The proposed configuration of the WFMOS A&G System. A coherent fiber
bundle reimages the focal plane onto the A&G Camera. .................................................... 31
Figure 3.9-1: The Prime Focus Instrument ........................................................................... 32
Figure 3.9-2: The Rotating Portion of the PFI ...................................................................... 33
Figure 3.9-3: The PFI Fixed Structure ................................................................................... 33
Figure 3.10-1. Positioner Bench Populated with One Module and a Single Positioner. 35
Figure 3.10-2: Positioner Patrol Region Overlap. The black dashed lines indicate the
patrol regions of adjacent positioners, showing there is complete coverage of the
populated field of view. The distance between adjacent positioners, d, is 8 mm, while
the diameter of the Patrol Region, 2R, is 9.5 mm. Blue and orange represent the two
stages of the positioner motors (see text).............................................................................. 36
Figure 3.10-3: Optical coupling efficiency versus distance from the center of the field of
view. The plot shows the field coverage of the positioner array. Coupling includes the
optical performance of the WFC and the numerical aperture of the fiber, but does not
include seeing or WFC internal flexure................................................................................... 37
Figure 3.10-4: The Prototype Cobra Fiber Positioner ......................................................... 38
Figure 3.10-5: Rotary Squiggle Motor Motive Force Schematic........................................ 38
Figure 3.10-6: Patrol Region of a single fiber positioner (top view). The two motors in
each positioner have axes that are offset from one another, allowing the fiber tip to
travel anywhere within the patrol region................................................................................. 39
Figure 3.10-7: Positioner System Block Diagram ................................................................ 40
Figure 3.10-8: Prototype Positioner Testbed. A light source illuminates a fiber optic
mounted in the Cobra positioner unit under test. A CCD camera accurately measures
the position of the fiber tip......................................................................................................... 42
Figure 3.11-1: Schematic of the fiber system from the positioners to the spectrograph.
Pictures of key hardware from risk-reduction activities are also shown............................ 43
Figure 3.11-2: Fiber Throughput and the Contribution from Various Components........ 44
Figure 3.12-1: The optical design of a single WFMOS spectrograph, shown here as
configured for the GAHR survey. The diameters of the major optical elements are
shown in millimeters. ................................................................................................................. 48
Figure 3.12-2: CAD model of one of the three identical spectrographs, shown here as
configured for the GAHR survey. The table is approximately 5 m × 3 m.......................... 48
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