Parameters

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• Parameters

Design Considerations at Phase A and Beyond
Cassegrain Ultraviolet Brazilian ESO Spectrograph
Design team Beatriz Barbuy Bruno Castilho Hans
Dekker Bernard Delabre Clemens Gneiding Jean-Louis
Lizon Vanessa B. P. Macanhan Roland Reiss Joël
Vernet Phase A team Florian Kerber, Gero
Ruprecht, Harald Kuntschner
Challenges in UV Astronomy, October 2013 Paul
Bristow
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Overview

• Requirements that drive the design
• Achieving high efficiency
• Opto-mechanical design
• Slicer
• Detector Array
• Optical Bench
• Atmospheric Dispersion Compensation
• Calibration
• Summary

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Not so many parameters

• In geometry theres no 3D object much simpler
  than a CUBE (fully described by one parameter)
• Except maybe a SPHERE (ESOs already got one,
  nearly)
• or a TETRAHEDRON.
• Simple means
• Quicker
• Less risk
• Cheaper
• Easier to operate
• Easier to calibrate

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TTTLRS

• Top Three Top Level Requirements
• Significantly improve upon throughput (or better
  S/N) of existing ground based UV spectrographs
  USP!
• Achieve R20,000
• Cover the wavelength range 310-360nm (302-385nm)
• Actually four
• VLT gt
• 8m Diameter collecting area
• Paranal seeing and extinction
• Interface with VLT infrastructure
• Campaign mode

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Achieving high efficiency

• Atmosphere
• Optical design
• Cass focus
• Slicer (no AO)
• Single dispersive element
• Minimum surfaces
• Grating
• Detector

Cassegrain 77 Nasmyth 65
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Comparison to FORS2,UVES X-shooter
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Choices arising from TTTLRs
Design Aspect Implications
Cassegrain Flexure away from Zenith
Slicer (no AO) Complexity of AG DRS Noise
No X-dispersion or pre-dispersion Resolution/wavelength range
Minimal surfaces Difficulty/cost of optics
High efficiency grating New technology/cost
High QE detector New technology/cost
Ground based/Paranal Atmosphere
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Evolving Opto-mechanical Design Detector Array

• Long detector array
• 3 or 4 4K 2K 15µm 15µm
• 250mm x 30mm (200pix gaps)
• Large (but feasible) detector vessel
• One mode (plus interlace)
• No pre-disperser, grating operating in 1st order
  gtno tuneable wavelength range (without losing
  efficiency)
• Several methods of recovering the wavelengths
  that fall into the detector gaps are under
  consideration

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Evolving Opto-mechanical Design Slicer

• Phase A slicer design had three very efficient
  slitlets
• Smaller slitlets
• Larger wavelength range for given detector array
  size and resolving power
• More slitlets needed gt signal spread over more
  pixels
• Detailed Simulations to investigate optimal
  number of slitlets and their widths
• Binning, RON, Dark current
• Integration times, Targets
• Seeing, Sky brightness

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Evolving Opto-mechanical Design Slicer
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Evolving Opto-mechanical Design Slicer

• MUSE style slicer, gt7 slices lt0.3 slitlet
  widths

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Evolving Opto-mechanical Design Optical Bench
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Evolving Opto-mechanical Design Camera and DV
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Evolving Opto-mechanical Design Pre-slicer
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Evolving Opto-mechanical Design ADC?

• Observe along parallactic (default)
• Flexure easier to handle
• Airmass restrictions anyway

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Evolving Opto-mechanical Design Calibration Unit

• Talk by Florian Kerber on LDLS for flats
• Potential wavecal sources, Hollow Cathode Lamps
• Th-Ar or Th-Ne
• Pt/Cr-Ne
• Tellurics for absolute wavelength ZP?
• Simultaneous wavelength calibration?
• Repeatability/stability
• Automatic flexure compensation
• Stray light
• To be decided

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Summary

• The CUBES design is dedicated to providing
  significant SNR improvement relative to existing
  ground based UV spectrographs
• CUBES will be easy to build, easy to operate and
  maintain and easy to calibrate

Slicer No. slicesgt7 slitlet widthslt0.3
Transmission grating 3200mm-1 1st order Ruled width260mm gt80_at_320nm
Detector Array 4 4K 2K 15µm15µm250mm x 30mmQEgt85 _at_320nm Dark current lt0.001e-/pix/sRON lt2.5e-
Wavelength Range 302-390nm (TBC)
Resolving Power 20,000
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End of Talk