parameters challenges in uv astronomy, october 2013 paul bristow design considerations at phase a...
TRANSCRIPT
Parameters
Challenges in UV Astronomy, October 2013
Paul Bristow
Design Considerations at Phase A and Beyond
Design team:Beatriz BarbuyBruno CastilhoHans DekkerBernard DelabreClemens GneidingJean-Louis LizonVanessa B. P. MacanhanRoland ReissJoël Vernet
Phase A team: Florian Kerber, Gero Ruprecht, Harald Kuntschner
CassegrainUltravioletBrazilianESOSpectrograph
Challenges in UV Astronomy – October 2013
Requirements that drive the design Achieving high efficiency Opto-mechanical design
SlicerDetector ArrayOptical BenchAtmospheric Dispersion CompensationCalibration
Summary
Overview
Challenges in UV Astronomy – October 2013
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:QuickerLess riskCheaperEasier to operateEasier to calibrate
Not so many parameters
Challenges in UV Astronomy – October 2013
Top Three Top Level RequirementsSignificantly improve upon throughput (or better S/N) of
existing ground based UV spectrographs – USP!Achieve R≥20,000Cover the wavelength range 310-360nm (302-385nm)
Actually four…:VLT =>
• 8m Diameter collecting area• Paranal seeing and extinction• Interface with VLT infrastructure• “Campaign mode”
“TTTLRS”
Challenges in UV Astronomy – October 2013
Achieving high efficiency
Atmosphere Optical design
Cass focusSlicer (no AO)Single dispersive
elementMinimum surfaces
Grating Detector
16:34:58
Positions: 1-16 19-Jul-12
150.00 MM
~20%
Airmass= 1.01.3
1.8Cassegrain ~77%Nasmyth ~65%
Challenges in UV Astronomy – October 2013
Choices arising from TTTLRs
Design Aspect Implications
Cassegrain Flexure away from Zenith
Slicer (no AO) Complexity of A&G; 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
Challenges in UV Astronomy – October 2013
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
Challenges in UV Astronomy – October 2013
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 powerMore slitlets needed => signal spread over more pixels
Detailed Simulations to investigate optimal number of slitlets and their widths:Binning, RON, Dark current Integration times, TargetsSeeing, Sky brightness
Challenges in UV Astronomy – October 2013
Evolving Opto-mechanical Design: Slicer
7 x 0.25”
3 x 0.45”
5 x 0.35”
7 x 0.35”
V=19 QSO
MUSE style slicer, >=7 slices; <=0.3” slitlet widths
Challenges in UV Astronomy – October 2013
Observe along parallactic (default)Flexure easier to
handle
Airmass restrictions anyway
Evolving Opto-mechanical Design: ADC?
Challenges in UV Astronomy – October 2013
Evolving Opto-mechanical Design: Calibration Unit
Talk by Florian Kerber on LDLS for flats Potential wavecal sources, Hollow Cathode Lamps:
Th-Ar or Th-NePt/Cr-Ne
Tellurics for absolute wavelength ZP? Simultaneous wavelength calibration?
Repeatability/stability• Automatic flexure compensation
Stray lightTo be decided…
Challenges in UV Astronomy – October 2013
Summary
Slicer No. slices>=7; slitlet widths<=0.3”
Transmission grating ~3200mm-1; 1st order; Ruled width~260mm; >80%@320nm
Detector Array 4 4K × 2K × 15μm×15μm;250mm x 30mmQE>85% @320nm;Dark current <0.001e-/pix/s;RON <2.5e-
Wavelength Range 302-390nm (TBC)
Resolving Power 20,000
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