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VEGA: Second Generation

VEGA: Second Generation. VEGA: SECOND GENERATION First studies … Philippe Berio , Denis Mourard , Jean- michel Clausse , Alain Spang. VEGA Meeting, 6-7 February 2012. VEGA: Second Generation. Why ?. Why an instrument of second generation ?

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VEGA: Second Generation

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  1. VEGA: Second Generation VEGA: SECOND GENERATION First studies … Philippe Berio, Denis Mourard, Jean-michelClausse, Alain Spang VEGA Meeting, 6-7 February 2012

  2. VEGA: Second Generation Why ? • Why an instrument of second generation ? • Installation of OA system in the next 2 or 3 years • Saturation problems with photon counting detectors (high flux or small D/r0) • Low visibilities measurements are difficult • Increase the limiting magnitude • Increase the measurements precision • Combine 6 telescopes simultaneously Low noise analog detectors Single-mode spatial filters VEGA Meeting, 6-7 February 2012

  3. VEGA: Second Generation OA for CHARA Performances attendues en bande H • OA characteristics • OA installed in the telescopes • Shack-Hartmann sensors • Modal correction • 30 sub-pupils / 19 actuators • Scheduling • PDR 60 days after funding agreement • Systems should be ready for scientific observations 2 years after PDR • Expected performances in the visible (700nm) • Strehl ≈30% for r0=12cm • => coupling ≈25% • Strehl ≈6% for r0=6cm • => coupling ≈5% VEGA Meeting, 6-7 February 2012

  4. VEGA: Second Generation Spatial filtering • 3 possible solutions : • with single mode optical fibers • easy transportation • good transmission over Dl<100nm • with integrated optics • Compact system (multi-axial combiner) • active modules (OPD modulation, …) • transmission loss (2-3dB) • with pinholes • not studied • Collaboration: • with LPMC : optical fibers and integrated optics • First meeting (20 January 2012) • with IPAG (P.Kern): integrated optics VEGA Meeting, 6-7 February 2012

  5. VEGA: Second Generation Analog detectors • Commercial solutions: • ORCA-flash4 from Hamamatsu, NEO sCMOS from Andor • 100 frames per second • quatum efficiency < 70% • RON > 1.3 e- • > 4Mpixels • OCAM2: • Low noise camera developped by IPAG-LAM • 1500 frames par second maximum • quantum efficiency> 90% between 600nm and 800nm • RON ~ 0.13e- • 240x240 pixels VEGA Meeting, 6-7 February 2012

  6. VEGA: Second Generation Concept VEGA Meeting, 6-7 February 2012

  7. VEGA: Second Generation Expected performances with ORCA-Flash4 • SNR expression • Parameters : • Quatum efficiency: 70% • CHARA Transmission : 3% • Spectro Transmission : 46% • OA Transmission : 80% • Polar Transmission : 50% • RON : 1.3 • 4 pixels per fringe • FOV: 2l/D • Dl: 15nm @ 700nm • npix: 48x214 • DIT: 15ms • M: 40000 (10 minutes) • Vinst: 0.7 • RatioPhot: 20% V*=0.1 V*=1 => Gain of 2 magnitudes wrt current VEGA VEGA Meeting, 6-7 February 2012

  8. VEGA: Second Generation Expected performances with OCAM2 • SNR expression • Parameters: • Quatum efficiency: 90% • CHARA Transmission : 3% • Spectro Transmission : 46% • OA Transmission : 80% • Polar Transmission : 50% • RON : 0.13 • 4 pixels per fringe • FOV: 2l/D • Dl: 15nm @ 700nm • npix: 48x214 • DIT: 15ms • M: 40000 (10 minutes) • Vinst: 0.7 • RatioPhot: 20% V*=0.1 V*=1 => Gain of 4 magnitudes wrt current VEGA VEGA Meeting, 6-7 February 2012

  9. VEGA: Second Generation Performances • SNR expression of the power spectrum developed by Gordon&Buscher (2011) • cross-terms between RON and photon noise • should be considered as a fringe detection SNR (SNR>3) Current VEGA Current VEGA => Photon-counting detectors are still interesting for faint objects VEGA Meeting, 6-7 February 2012

  10. VEGA: Second Generation Conclusions • OA/Optical Fiber/OCAM2 solution seems interesting • => theoretical limiting magnitude ~ 11 • But: • 240 pixels maximum in the spectral direction=> spectral bandwidth 3x smaller than for the current VEGA • It should be possible to create 2 or 3 parts of the spectrum on the detector simultaneously (in the spatial direction) • Good transmission of the fibers over a spectral bandwidth of 100nm only • 3 or 4 kind of optical fibers are needed if we want to keep the possibility to observe from 550nm to 850nm VEGA Meeting, 6-7 February 2012

  11. VEGA: Second Generation Perspectives • Next steps • Use the OA simulator of M.Ireland • confirmed the estimated performances in the visible • Progress in the performance budget • Test of an analog detector this year • check the expected quantum efficiency and the RON • Work on the definition of spatial filters • in collaboration with LPMC and IPAG • start tests in laboratory (in 2012 ?) • Study the possibility to use an analog detector for bright objectsanda photon-counting detector for faint objects • Astrophysical program (major science cases) • 4T or 6T ? Spectral resolution? Spectral band? VEGAS (VEGA Secondgeneration) VEGA Meeting, 6-7 February 2012

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