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A Detector Upgrade for LDSS3. Mike Gladders Jacob Bean (on the phone) with Andreas Seifart , Josh Frieman , John Carlstrom. LDSS-3. continues to be a scientifically productive and reasonably in-demand instrument

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a detector upgrade for ldss3

A Detector Upgrade for LDSS3

Mike Gladders

Jacob 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
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 Concern is a (modest) Loss of Area

Existing detector footprint



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

New detector footprint


600 – 1100 nm is 2200 pixels @ R = 2000


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 LDSS3

predicted water absorption

predicted methane absorption

Bean et al. (2011)

  • 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

Competitive Landscape

  • Gemini North + GMOS with planned HammamatsuCCDs 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

Upgrade project

  • 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