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Parameters

Design Considerations at Phase A and Beyond. C assegrain U ltraviolet B razilian E SO S pectrograph. Parameters. Design team : Beatriz Barbuy Bruno Castilho Hans Dekker Bernard Delabre Clemens Gneiding Jean - Louis Lizon Vanessa B. P. Macanhan Roland Reiss Joël Vernet

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Parameters

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  1. Design Considerations at Phase A and Beyond Cassegrain Ultraviolet Brazilian ESO Spectrograph Parameters Design team: Beatriz Barbuy Bruno Castilho Hans Dekker Bernard Delabre Clemens Gneiding Jean-Louis Lizon Vanessa B. P. Macanhan Roland Reiss JoëlVernet Phase A team: Florian Kerber, GeroRuprecht, HaraldKuntschner Challenges in UV Astronomy, October 2013 Paul Bristow

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

  3. Not so many parameters • In geometry there’s no 3D object much simpler than a CUBE (fully described by one parameter): • Except maybe a SPHERE (ESO’s already got one, nearly); • or a TETRAHEDRON…. • Simple means: • Quicker • Less risk • Cheaper • Easier to operate • Easier to calibrate

  4. “TTTLRS” • Top Three Top Level Requirements • Significantly improve upon throughput (or better S/N) of existing ground based UV spectrographs – USP! • Achieve R≥20,000 • Cover the wavelength range 310-360nm (302-385nm) • Actually four…: • VLT => • 8m Diameter collecting area • Paranal seeing and extinction • Interface with VLT infrastructure • “Campaign mode”

  5. Achieving high efficiency • Atmosphere • Optical design • Cass focus • Slicer (no AO) • Single dispersive element • Minimum surfaces • Grating • Detector Airmass= 1.0 1.3 1.8 Cassegrain ~77% Nasmyth ~65% ~20%

  6. Comparison to FORS2,UVES & X-shooter

  7. Choices arising from TTTLRs

  8. 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 =>no tuneable wavelength range (without losing efficiency) • Several methods of recovering the wavelengths that fall into the detector gaps are under consideration

  9. 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 => 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

  10. Evolving Opto-mechanical Design: Slicer

  11. Evolving Opto-mechanical Design: Slicer • MUSE style slicer, >=7 slices; <=0.3” slitlet widths 3 x 0.45” 5 x 0.35” 7 x 0.25” 7 x 0.35” V=19 QSO

  12. Evolving Opto-mechanical Design: Optical Bench

  13. Evolving Opto-mechanical Design: Camera and DV

  14. Evolving Opto-mechanical Design: Pre-slicer

  15. Evolving Opto-mechanical Design: ADC? • Observe along parallactic (default) • Flexure easier to handle • Airmass restrictions anyway

  16. 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…

  17. 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

  18. End of Talk

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