The following tables show the intended performance characteristics of DEIMOS as of 4 Feb 1999.

Table 1: Estimated Physical and Optical Characteristics

Location Right Nasmyth platform, Keck II; removable from focus
Layout Two cameras fed from common collimator
Rotator 740° rotation
User access Slit masks, all gratings and all filters
Guiding system One guider; ~10 sq arcmin FOV; slit-viewing and offset modes are both available
Spectrograph flexure control Two-coordinate beam-steering with closed-loop feedback
Flexure Goal is 0.25 px rms motion over typical integration (with flexure control system on, 2px rms open loop)
Slit masks 13 in cassette;
cylindrical radius of curvature matched to focal plane curvature
Slitlet options Slitlets of arbitrary size and orientation
Dispersive elements 6×8 in and 8×12 in gratings;
3 slots
Imaging option Silvered flat mirror replaces grating
Filters 6.5×6.5 in glass filters;
7 slots; BVRI, ``clear,'' and 2 ``user'' slots
Collimator focal length 86.50 in
Camera focal length 15.00 in
Beam diameter 6.33 in for 10.95 m primary;
5.79 in for 10.02 m primary
Monochromatic f/ratio f/2.358 for 11.00 m primary;
f/2.586 for 10.02 m primary
Polychromatic f/ratio f/1.29
Scale at detector 0.00759 arcsec/µm;
0.119 arcsec per 15µm px
CCD detector array 8192x8192 px (15 µm px);
2x4 mosaic of 2Kx4K CCDs
Angular field radius of camera 11.40°
Camera glass transmission 97% for lambda > 5200 Å;
88% at 3900 Å;
93% at 4400 Å
Total camera throughput 85% at lambda > 5200 Å;
77% at 3900 Å
(including coatings and transmission)

Note:

Table 2: Estimated Imaging Performance

Field shape Rectangular with 2 lopped-off corners;
sliver out of long side
Outer dimensions of rectangular field 16.7 arcmin×5.0 arcmin
Area lost to CCD mosaic gaps 0.4 arcmin×5.0 arcmin
CCD pixel scale 0.119 arcsec per px (15µm px)
Wavelength range (imaging) 4100 Å - 11,000 Å
Standard filters¹ BVRI + 2 user filters
Throughput at 6000 Å² 40% (including telescope)
Image size (including telescope aberrations) B band (0.5 arcsec seeing): 0.56 arcsec FWHM
V-->I bands: 0.54 arcsec FWHM
Expected count rate³ 800 e- per sec in V band at 21.0 mag
Mode changes 30 sec changeover between imaging and spectroscopy

Notes:

  1. Slightly redshifted B band with blue edge at ~4000 Å.
  2. End-to-end throughput including telescope and assuming CCD QE=0.6 and all reflecting surfaces are silver coated. No filter or atmosphere included.
  3. V mag is light entering telescope. Rate is through standard V filter.

Table 3: Estimated Spectroscopic Performance

Total slit length 16.7 arcmin
Usable slit length¹ 16.3 arcmin
Total number of slitlets 85 10-arcsec slitlets with 1.5 arcsec gaps
CCD detector scale 0.119 arcsec per px (15µm px)
Wavelength range (spectra) 4100 Å -- 11,000 Å
Order blocking filters TBD
Slit widths User selectable by choice of mask;
long-slits will provide variety of fixed widths
Design slit widths 0.75 arcsec nominal, 0.5 arcsec good seeing
Current gratings (all 6 x 8 in) 600 l/mm (7500 Å blaze);
900 l/mm (5500 Å blaze);
1200 l/mm (7500 Å blaze);
Number of grating slots 3 slots available
Corresponding dispersions 0.65 Å/px, 0.44 Å/px, and 0.33 Å/px
Spectral lengths (8000 px) 5300 Å, 3840 Å, and 2630 Å
FWHM resolutions 3.5 Å, 2.1 Å, and 1.1-1.6 Å for 0.75 asec slit
Throughput at 6000 Å² 29% (including telescope)
Count rate at 6000 Å 1.0 e- per sec at V = 21.0
S/N on faint stellar objects in one hour³ 5:1 for V = 24.0;
12:1 for V = 23.0;
21:1 for V = 22.0

Notes:

  1. Slit length subtended by detector pixels.
  2. End-to-end throughput including telescope assuming CCD has QE=0.6 and all reflecting surfaces are silver coated.
  3. S/N per pixel for 3600 s integration, 0.75 slit, on point source with 0.7 arcsec seeing at 5500 Å and 0.65 Å/px (600 l/mm grating). V is magnitude of light going through slit. Assumed V sky brightness is 21.25 mag/arcsec².