Astronomy 920 Commissioning of the Prime Focus Imaging Spectrograph Meeting 4 CCD Detector; Signal/ Noise Model Ken Nordsieck Sept 30, 2005 Ast 920 Meeting 4

Grating Optics CCD Detectors Signal/ Noise Geometry Efficiency Gain and Fullwell Readout Noise and Speed Signal/ Noise Target and Sky Photon noise Readout Flatfield Sept 30, 2005 Ast 920 Meeting 4

CCD Geometry 3 CCD's each 2048 x 4096 15 micron square pixels, 62 x 93mm mosaic gap ~90 pixels CCD focal plane scale 177 microns/ arcsec F/2.2: Effective focal length = 11000x 2.2 = 24,200 mm FPS = (206265 arcsec/rad)/ 24200mm= 8.5 arcsec/mm 7.8 pixels/ arcsec since seeing ~ arcsec, this is "oversampled", bin ~2 pixels 8 arcmin FOV 4096 2048 Dispersion Sept 30, 2005 Ast 920 Meeting 4

Put UV CCD in the right place Efficiency The 3 CCD’s have somewhat different efficiencies Put UV CCD in the right place SALT 03 SALT 04 SALT 06 Sensitivity350 nm 400 nm 500 nm 650 nm 900 nm 1000 nm (%) 79.9 86.0 85.0 75.5 45.4 10.8 (%) 66.5 79.2 79.6 74.4 46.8 10.7 (%) 50.4 75.6 81.8 74.8 48.7 10.6 Readout noise: (e-/pix) 2.3 2.2 2.0 2.4 2.0 2.0 Sept 30, 2005 Ast 920 Meeting 4

Binning, Gain and Fullwell Pixel read out by shifting rows into serial shift register ("parallel shift"), then shift pixels in that register into amplifier "Prebin" pixels in y-direction by doing several parallel shifts before reading out serial register Prebin in x direction by doing several serial shifts before doing an amplifier sample Maximum signal ("fullwell") set by "depth" of physical pixel (150,000 e-), serial register (3x pixel), or amplifier (4x pixel). Each amplifier converts voltage to digital value (ADU) ADU = e- / Gain max ADU = 216 PFIS has two Gain setting, Bright and Faint use Bright to collect more photons/ readout PFIS has separate "image" and "storage" halves, which may be clocked separately, for high-speed "frame transfer" Each PFIS CCD has two amplifiers, reading out 1024x4096 pixels Sept 30, 2005 Ast 920 Meeting 4

Readout Noise and Speed Associated with each bin readout is a readout noise. Depends on gain and readout speed: 1 2 3 4 5 6 6.34 FAST FAINT 6.59 6.78 6.15 5.88 7.82 4.81 10.04 BRIGHT 10.20 10.68 9.82 9.18 10.81 9.57 2.51 SLOW 2.46 2.42 2.33 2.43 2.91 2.50 3.73 3.74 3.78 3.62 3.56 4.14 3.54 Use fast readout to minimize overhead time when need many readouts (bright objects, polarimetry, Fabry-Perot Fast Readout: 3 microsec/ bin. 1x1 in 12.5 sec Slow Readout: 10 microsec/bin. 1x1 in 43 sec Sept 30, 2005 Ast 920 Meeting 4

Signal/ Noise Signal: Noise S = Flux * Effective Area * Throughput * Exposure units: detected photons Throughput: mirrors * lenses * slit thoughput * grating eff * CCD eff Noise N = sqrt (Star + Ssky + RO2) Sept 30, 2005 Ast 920 Meeting 4