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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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slide1

VEGA: Second Generation

VEGA: SECOND GENERATION

First studies …

Philippe Berio, Denis Mourard, Jean-michelClausse, Alain Spang

VEGA Meeting, 6-7 February 2012

slide2

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

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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

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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

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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

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VEGA: Second Generation

Concept

VEGA Meeting, 6-7 February 2012

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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

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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

slide9

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

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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

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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