A Detector Upgrade for LDSS3

Mike GladdersJacob Bean (on the phone)

with Andreas Seifart, Josh Frieman, John Carlstrom

LDSS-3

• continues to be a scientifically productive and reasonably in-demand instrument

• however, LDSS-3 was designed as a high-throughput red sensitive MOS: this goal was never realized due to detector limitations

• we now have an opportunity to finally make LDSS-3 look like it was intended to be, and to open new scientific opportunities thereby

The Proposal• To replace the current 4kx4k CCD electronics with a

new detector and electronics drawn from the system built for the Dark Energy Camera

• offers dramatic increases in throughput at 8000-10500A, as well as essentially no fringing in the red

• will finally allow nod-shuffle observations• proposed electronics are tuned to these devices and will allow fast

readout (unbinned, full frame, 7 e- noise in 17 seconds) and slow readout (unbinned, full frame, 2.5e- in 80 seconds) with binning, rastering, charge shuffling etc as well

• upgrade to be fully funded by Chicago – the money is effectively in hand and we are ready to begin

Proposed Detector Upgrade: Primary Benefit is Throughput!

8.3’

Existing detector footprint

Proposed Detector Upgrade: Primary Concern is a (modest) Loss of Area

600 – 1100 nm is 2200 pixels @ R = 2000

6.4’

New detector footprint

Proposed Detector Upgrade: Primary Concern is a (modest) Loss of Area

Secondary Benefits and Concerns•Macroscopic nod-shuffle observations with LDSS-3 were never realized, despite significant early efforts; this mode should be possible with the new chip and electronics, and allow high-density micro-aperture spectroscopy in the far red; this requires dispersion along the short axis of the chip.Normal spectroscopic observations – single objects or MOS – requires dispersion on the long axis of the slit to maintain the current capabilities.We propose to ensure rapid rotation of the detector with an appropriate mount design; an extra ~1.5 inches of mount space between the dewar and the instrument that is currently occupied by an aluminum ring allows this

•the rapid readout in imaging mode should facilitate efficient alignment on sky; we propose to put effort into improving the alignment times to < 1 minute, realizing effective gains in throughput by minimizing overheads

•these thick chips will have an enhanced CR rate; with the enhanced sensitivity and rapid and low-noise readout we do not expect this to be problematic

•focal depth changes due to penetration of photons in the far red in these thick chips is not a significant concern

Science Opportunities

•exoplanet transit spectroscopy – will allow us to probe the critical 850-1000nm window

•spectroscopy of distant galaxies:

• early type (cluster?) galaxies: z~0.9 limit z~1.4 (H&K to G-band region)

• emission line galaxies: z~1.2 z~1.7 ( [OII]3727 )

z~5.3 z~6.7 ( Ly-A )

•spectroscopy of distant GRBs: as Ly-A in galaxies above

•spectroscopy of distant SNe yields improvements in redshift similar to that for early-type galaxies

Need for red coverage with LDSS3predicted water absorption

predicted methane absorption

• 900 – 1000 nm the only region water can been seen from the ground• Instrument throughput critical: need >108 photoelectrons per spectral

bin in just a few hours

Bean et al. (2011)

Competitive Landscape•Gemini North + GMOS with planned Hammamatsu CCDs should have similar performance over a smaller FOV. This upgrade has been repeatedly delayed.

•new LRIS Red III dewar on Keck is supposedly ‘LBNL CCDs’. Available documentation suggests it is 2x better than DEIMOS at 1um. Comparable to proposed, except at >9500A

• The project is to build and integrate a complete CCD system (housing, dewar, detector, and electronics)

• Jacob Bean’s group will lead the project, Andreas Seifahrt will be the instrument scientist

• Cost excluding the detector is estimated at $50k including electronics spares etc.; will be covered by U. Chicago Department of Astronomy & Astrophysics funds

Upgrade project