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P.I.: J. S. Miller, M. Bolte, R. Guhathakurta, D. Zaritsky (UCO/Lick
Observatory)
The ESI instrument is a versatile, multi-mode spectrograph and imager,
with high throughput one of its most important goals. Since ESI will not
begin commissioning until the end of August 1999, what follows is partly
design goals, rather than measured on-sky performance. There are two distinct
spectroscopic modes: a medium-resolution echellette mode with prism cross
dispersion; and a high-throughput mode using prism dispersion only. The
spectrograph modes will cover the full wavelength range of the Keck II silvered
mirrors (3900 to 11,000 Å) in a single exposure with a velocity resolution
of ~10-15 km/sec/pixel. The low-resolution, prism-only mode provides the
same spectral range, multi-object capability, and high throughput. ESI also
provides an imaging mode with a field of view of 3.0 arc-minutes. An Epps
refracting camera and a single 2K x 4K detector are used for all three modes.
The ESI collimator will be an off-axis paraboloid, similar to the collimator
in LRIS. A single 2K x 4K Lincoln Labs CCD with 15 micron pixels is used
with a Leach-2 CCD controller. A single, all-refracting camera, is used
for all three operating modes. There is a 1Kx1K PXL acquisition/guide TV
camera that views part of the slit plus a stationary, offset mirror. Three
5-position filter-wheels will be provided in the science beam: one in the
focal plane containing slits, and two beneath that providing either a mask
(for the echellette slits, which are all on a single slit plate) or filters.
Another wheel carries filters for the guide/acquisition camera. At any one
time, a single echellette grating is available, fixed in position and in
rotation. Changing gratings is a manual operation and normally will not
be done during the night. A flat mirror bypasses the grating for switching
to the prism-only (low-dispersion) mode. A second flat mirror bypasses both
the prisms and the grating to provide the imaging mode.
A page on sensitivities contains useful
information for planning exposure times, etc.
General specifications
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| Location |
Keck II Cassegrain (f/15) |
| Focal plane scale |
0.725 mm/arcsec |
| Scale at detector |
0.1542 +/- 0.0010 arcsec/pixel |
| Wavelength range |
0.39-1.1 microns |
| Detector |
MIT-LL 2048x4096 CCD, 15 micron pixels |
| CCD sensitivity |
QE of 10% (at 0.32 m), 61% (0.4 m), 82% (0.5 m), 80% (0.6 m), 77% (0.7 m),
69% (0.8 m), 45% (0.9 m), 11% (1.0 m) |
| Readout electronics |
Leach 2 DSP programmable |
| Readout modes |
Single or dual amplifier; slow, normal, and fast (the default) modes |
| Readout times |
39 sec (dual-amp, default [fast] speed)
70 sec (simgle amp, default speed) |
| Readout noise |
2.5 electrons/pixel (normal readout speed) |
| Grating |
175 lines/mm, 32.3° blaze angle |
| Cross dispersion |
Two prisms, first used in double-pass mode. |
| Slit/filter wheels |
Three, only first (slit wheel) in focal plane.
Five "slots" in each wheel. Each slot can accomodate up to three
filters. Normally one slot is left clear in each wheel. |
| Wavelength calibration lamps |
Xe, HgNe, CuAr, quartz |
| Guider |
Slit viewing with offset field
1024x1024 Photometrics PXL CCD
Total FOV 3x3 arcmin.
0.233 arcsec/pixel
50x50 mm filters, initially only ND filter provided. |
Echellette mode |
| Wavelength range |
0.39-1.1 microns |
| Spectral resolution |
11.4 km/sec/pixel |
| Slit length |
20 arcsec |
| Slit widths |
0.3, 0.5, 0.75, 1.0, 1.25, 6 arcsec
(all on same slit plate, selectable using mask in second wheel) |
| Order blocking filters |
None |
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Low-dispersion mode |
| Wavelength range |
0.39-1.1 microns |
| Spectral resolution |
R=6000 (0.39 microns) to R=1000 (1.1 microns) |
| Slit length |
8 arcmin |
| Slit widths |
0.5, 0.75, 1, 1.25, 6 arcsec (each on a separate slit plates).
Currently only the 1 and 6 arcsec slits are available. |
| Order blocking filters |
None needed; dispersion provided by prisms, which
have no higher-order spectra. |
| Slitmasks |
Not available initially. |
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Imaging mode |
| Field of view |
2x8 arcmin full field
2.1x3.5 arcmin for 93x154 mm filters) |
| Scale |
0.1542 +/- 0.0010 arcsec/pixel |
| Filters |
B, V, R, I (93x154 mm; 128x212 arcsec FOV)
full-field R filter (2x8 arcmin FOV)
holders for two 100x100 mm filters (138x138 arcsec)
holders for three 50x50 mm filters (69x69 arcsec) |
User interface
| Control electronics |
intelligent Galil controllers, parallel stage control |
| Computer |
Sun Ultra 2, OpenWindows |
| Image display |
FIGDISP with tcl/tk GUI |
| Control GUI |
Dashboard (tcl/tk-based) |
| Data reduction |
IRAF, IDL, Vista, custom echelle reduction software |
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