DEIMOS Notes for Observing Assistants

Description

DEIMOS is a general-purpose, faint-object, multi-slit, double-beam, visible-wavelength imaging spectrograph at the Nasmyth focus on Keck II. DEIMOS features wide spectral coverage (up to 5000 Å per exposure), high spectral resolution (down to ~1 Å), high throughput, and relatively wide field of view (81.5 arcmin² field).

Summary

Type: Dual-beam, multi-object spectrograph
Wavelength range: optical
Spectrograph type: slitmask
Detector array: 8 × ( 4k × 2k) CCDs
Rotator: built in
Position: K2 RNAS
Built at: UCO/Lick
Optimized for: Surveys of distant galaxies
GUI control: Dashboard (similar to ESI)

Guider

PXL 1024×1024 pixel at 0.21 arcsec/px
Field of view shows pickoff mirror at bottom 1/3 and slitmask on top 2/3
Slow readout like ESI
Displays significant pattern noise in 2×2 binning readout mode.
Get good reflection off slitmasks; guiding on slitmask OK
TV guider flexure is significant

Rotator

Entire instrument rotates
Limits of rotation are -330° < ROTPPOSN < +400° (two complete revs)
Slew speed is about 2m 15s per 1 revolution
Tracking excellent through zenith

Pointing Origins

See also: KSD40-style drawing of focal plane
REF is on center of pickoff mirror (AUTOFOC here)
SLIT is centered on the longslit position
IMAGE is directly above the slit (send faint longslit targets here)
DEIMOS is at slitmask center (send slitmask centers here)
TVCENTER is at center of guider (512,512)
MIRA will be used for telescope focus

Focus

AUTOFOC and MIRA work well
Secondary tilt compensations should be minimal
Should not need to focus as often as with LRIS
Probably no telescope focus difference between imaging and spectroscopy modes

Eavesdropping

OA can run DEIMOS dashboard from DCS GUI