Astronomy 920 Commissioning of the Prime Focus Imaging Spectrograph

1
Astronomy 920Commissioning of the Prime Focus
Imaging Spectrograph

• Meeting 5
• Signal/ Noise Model Planning Tool
• Ken Nordsieck

2
Signal/ Noise

• Signal
• Star Flux Atmos Effective Area Throughput
  Bandpass Exposure
• Ssky Brtness Atmos Solid Angle of Res El
  Effective Area Throughput Bandpass Exposure
• Flux (erg/s-cm2-Ang) / h?
• Brtness (erg/s-cm2-arcsec2-Ang) / h? (also use
  for diffuse target)
• units detected photons
• Noise
• N sqrt (Star Ssky RON2)

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Sky, Atmosphere

• For Details
• http//www.sal.wisc.edu/PFIS/docs/archive/protecte
  d/pfis/3170/3172AS0005-spec-sim-1.1.pdf
• Atmospheric Extinction
• F(Earth) F(above atmos) 10-0.4 k(?)
• mag extinction k(Z, ?) X k(Z0, ?)
• airmass X 1/cos(Z) 1.25 /- 0.1 (Z 37
  /-6)
• UV Ozone Blue Rayleigh Red aerosols
• Sky Background
• Airglow atomic, molecular, lines
  pseudocontinuum
• (Na, O, O3, OH, etc). varies by 2x over solar
  cycle
• Zodiacal Light solar spectrum, lowest at
  ecliptic poles
• Moonlight solar spectrum. intensity varies
  with
• phase color intensity varies with Lunar
  angular elongation
• Seeing
• Sutherland 10, 50, 90 at zenith 0.6, 0.9,
  1.5
• FWHM FWHM (Zenith) X0.8
• Telescope imaging 0.6
• ? 10, 50, 90 image size 0.9, 1.2, 1.8

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Effective Area, Telescope Throughput

• Effective Area defined as area of illuminated
  primary
• Pupil projection of exit stop (in payload) back
  on primary mirror 11m diameter circle
• Central Obscuration about 3 m circle 83
• Obscuration due to pupil falling off primary
  mean over track 85
• 67 m2
• Telescope throughput Cmir
• - Primary Al
• Spherical Aberration Corrector 4x LLNL
  multilayer
• 80

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Spectrograph Throughput

• slit mirror lenses dispersor eff CCD eff
• if assume gaussian seeing I I0 e-(r/r0)2,
  linear slit of width 2rs throughput erfc(rs /
  r0)
• 1 fold mirror LLNL coating 96
• 16 air-glass interfaces 3 different
  anti-reflection coatings 83
• grating efficiency 50-90 etalon 70

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Bandpass

• By Mode
• Imaging effective width of filter
• Grating Spectroscopy ?? correspond to slit
• Fabry-Perot ?? of etalon
• For sky, use arcsec2 corresponding to resolution
  element
• Imaging, Fabry-Perot ?O area of seeing disk
• Grating Spectroscopy ?O (2 rs) (2 r0)
• To calculate readout noise, need number of bins
  corresponding to resolution element
• n ?O/(bxby / (7.8 pix/arcsec)2)
• RON RON/bin sqrt(n readouts)
• Done!