Astronomy 920 Commissioning of the Prime Focus Imaging ...khn/ast920/Astronomy 920.pdf · Astronomy 920 Commissioning of the Prime Focus Imaging Spectrograph Meeting 1 Organization;

Astronomy 920Commissioning of the Prime Focus Imaging Spectrograph

Index

Meeting 1. Organization; SALT OverviewMeeting 2. Introduction to PFISMeeting 3. VPH Gratings; MOS spectroscopyMeeting 4. CCD Detector; Signal/ Noise ModelMeeting 5. Signal/ Noise Model; Planning ToolMeeting 6. Signal/Noise; Fabry-PerotMeeting 7. SALT IRAF PackageMeeting 8. SALT IRAF Package IIMeeting 9. Slitmask PlanningMeeting 10. Longslit SpectroscopyMeeting 11. Polarimetry: Beamsplitter; Data formatsMeeting 12. Polarimetry: Waveplate Modulation; Calibration


Meeting 1Organization; Overview

Goals

• Learn of capabilities of Southern African Large Telescope and PFIS. Submit practice(or real) observing proposals.

• Become familiar with large telescope spectrograph design• Learn IRAF mosaic CCD reduction• Reduce and analyze data in support of commissioning: ~4 projects with ~2-member

teamsMaterials

• PFIS website http://www.sal.wisc.edu/PFIS/index.html• PFIS Observer’s Guide (Eric Burgh) http://www.sal.wisc.edu/~ebb/pfis/observer/• Instrument Model “PI Planning Tool” (Jeff Percival; Daniel Harbeck)

http://www.sal.wisc.edu/PFIS/index.html• SALT IRAF package (Me) on MADRAF, see Stephan Jansen• Lab and Commissioning Data, to be downloaded as it comes

For next week: access materials, form teamsMeeting format: lecture for <40 min/ discuss for 15. Email inputs for discussion

Syllabus• Intro (today)• Instrument Model

– Optics– Detector– Signal/ Noise Model

• Project Definition• Reduction/ Analysis

– CCD Bias/ Crosstalk/ Gain– Geometry– Spectroscopy

Payload Overview

• Tracker “Payload” equipment– Spherical aberration corrector (“SAC”). 4 Mirrors. Defines entrance pupil.– Calibration System– Moving baffle– Atmospheric Dispersion Corrector

• Ports– Acquisition/ Imaging camera (“SALTICAM”)– Fiber Feed Port– Auxiliary Port– PFIS (500 kg - 50% of weight budget)


Meeting 2PFIS Overview

• Optics Layout• VPH Gratings• Throughput• NIR upgrade path preserved by collimator allowing full 320 nm – 1.7 : wavelength

range + support structure• Assembly and Integration

PFIS Overview

• Major Prime Focus Instrument• Multimode/ remote controlled

– Narrow-Band Imaging 3200 – 9000 Ang– Multiobject (slitmask) grating spectroscopy 3200 – 9000 Ang– Fabry-Perot spectroscopy 4300 – 9000 Ang– All modes: polarimetry

• 3-CCD mosaic – High-Speed rapid readout

• Schedule– ship to Sutherland in a week– install late Sept– commission Oct - Nov

Slitmask Cutter

• Commercial laser • MOS: custom slits cut in carbon-fiber• Longslit: stainless steel, tilted and polished for viewing by SALTICAM/ slitviewer

optics• PI planning tool produces slitmask file for inclusion in proposal


Meeting 3VPH Grating Spectroscopy; MOS slitmask spectroscopy

• Grating Equation• Resolution• Why Large Telescope Spectrographs are Big• VPH Gratings• Where the spectra from different slitlets go• Ghosts

Grating Equation and Resolution

m 8 / 7 = sin " + sin $ = 2 sin " (Littrow) d8 / d$ = (7/m) cos $

angular size of monochromatic slit:)" = )2 Dtel / Dcol

)$ = )" cos " / cos $)8 (slit) = (7/m) cos " )2 Dtel / Dcol

at LittrowR = 8/)8 (slit) = 2 (Dcol / Dtel) tan " / )2

• Resolution does *not* depend on– diffraction order (!)– grating groove density (!)

• For fixed seeing, improve only by– going to higher grating angle (eg Echelle)– increasing the size of your collimated beam ($$)

• Note: for small telescopes, also worry about grating diffraction limit Rdif = Dgrat /7• For SALT/ PFIS: Dcol = 150 mm, Dtel / Dcol = 73.3

R = 5640 for 1 arcsec slit, 45 deg grating angle

VPH Gratings• Created by exposing holograph material (“DCG”) to interference pattern from laser• Index of refraction of DCG is modulated in space• Large; inexpensive; custom design; efficient at high groove density

Tunable “Blaze”• Peak efficiency is at Littrow => “Blaze angle” changes with "• If increase $ as tilt grating, can use grating at large range of central wavelengths =>

change camera angle = " + $

VPH Gratings - MOS Spectra• With slitlet MOS spectroscopy, each slitlet in the telescope focal plane goes through

the grating at a different angle, displacing the spectrum• perpendicular to dispersion, introduce out of plane angle ( to grating equation:

m 8 / 7 = cos ( (sin " + sin $)fixing 8 and ", as go off axis (( increase), $ must increase => central wavelength

decreases as (2

• parallel to dispersionfixing 8 and (, varying " about "0, ) sin $ = - ) sin " => monochromatic image looks like (slightly distorted) sky

Raw Data/ Artifacts• Neon arc lamp through slitmask at right• 2300 l/mm, " = 50º, $0 = 50º• 8 = 622 – 709 nm, central 666 nm, R (1 “) = 6495

• “Littrow Ghost”– dispersed light reflects off CCD, – back through camera (collimated), – diffracted off grating in reflection, (undispersed)– focused by camera back on CCD

=> focused image of telescope focal plane (inverted) at twice the grating angleMitigate: Take two spectra at different grating angles


Meeting 4CCD Detector; Signal/ Noise Model

• CCD Detectors– Geometry– Efficiency– Gain and Fullwell– Readout Noise and Speed

• Signal/ Noise– Target and Sky Photon noise– Readout– Flatfield

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

EfficiencyBinning, Gain and Fullwell

• Pixel read out by shifting rows into serial shift register ("parallel shift"), then shiftpixels in that register into amplifier

• "Prebin" pixels in y-direction by doing several parallel shifts before reading outserial 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

• Associated with each bin readout is a readout noise. Depends on gain and readoutspeed


Meeting 5Signal/ Noise Model; Planning Tool

Signal/ Noise• Signal:

Star = Flux * Atmos * Effective Area * Throughput * Bandpass * ExposureSsky = Brtness * Atmos * Solid Angle of Res El * Effective Area * Throughput *

Bandpass * ExposureFlux = (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)

Sky, Atmosphere• For Details:http://www.sal.wisc.edu/PFIS/docs/archive/protected/pfis/3170/3172AS0005-spec-sim-

1.1.pdf• Atmospheric Extinction:

– F(Earth) = F(above atmos) * 10-0.4 k(8)

– mag extinction: k(Z, 8) = X k(Z=0, 8)– 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”

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%

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%


Meeting 6Signal/Noise; Fabry-Perot

Signal/Noise: Bandpass• By Mode:

– Imaging: effective width of filter– Grating Spectroscopy: )8 correspond to slit– Fabry-Perot: )8 of etalon

• For sky, use arcsec2 corresponding to resolution element– Imaging, Fabry-Perot: )S = area of seeing disk– Grating Spectroscopy: )S = (2 rs) * (2 r0)

• To calculate readout noise, need number of bins corresponding to resolution element– n = )S/(bx*by / (7.8 pix/arcsec)2)– RON = RON/bin * sqrt(n * #readouts)

• Done!

Etalon Basics

Finesse and Free Spectral Range• PFIS etalons• With constant finesse, higher gap has higher resolution (larger order to get same

wavelength)• Can’t make one etalon do everything, since cannot practically scan more than about 6

microns (10 waves)• PFIS has 3 etalons, used in 4 modes• MR and HR always used with LR, for order blocking• Order Blocking• FP efficiency at spec in red, slightly below in blue

Scanning • PFIS control system allows arbitrary sets of discrete steps (equal exposures)

– linear scan for line profiles– dithering onto continuum for absorption lines

• Off axis, must take account of wavelength gradient due to cos 2center to edge gradient:

8(r)/ 80 = 1/ cos 2 ~ (1- .00365*(r/4’)2 ) (24 Ang at H")– Inside “bullseye”, wavelength changed by less than resolution:

D(bullseye) = 1.4’ (10,000/R)1/2– if object larger than bullseye, extend scan to cover same wavelengths– if object not round, pays to move telescope and rescan, instead of extending scan

Programs• FP best for programs requiring good spatial coverage, but few spectral

resolution elements• Velocity mapping• line flux maps

Quiz Question• Why did we go to all that expense to get large diameter etalons?

• Answer: – The etalons must be as large as the collimated beam in order to pass all the light. – The larger the collimated beam, the smaller is the off-axis angle 2 corresponding to

each off axis angle– The smaller 2 is, the larger is the "bullseye", so the effective field of view is larger.


Meeting 7SALT IRAF Package

Accessing SALT IRAF package

• Source (environment variable $salt)– Unix: /usr/local/salt– MAC: /usr/local/iraf/irafext/saltcl> salt [ loads salt task ]cl> help pfis [ lists pfis commands ]cl> pfis [ loads pfis subtask ]cl> cd working directory/yyyymmdd


Meeting 8SALT IRAF Package II

PFIS commands• Raw data

– name: Pyyyyddddssss.fits, ie P200510200079.fits– "multiextension" fits file, one for each of 6 amplifiers; open in DS9 with "openother/ open mosaic IRAF"

• Each stage of processing prepends a letter or two– Imaging: (pireduce, pmosaic) mrpP200510200097.fits– Spectroscopy: (psreduce) psP2.....

Imaging• pprepare (p)

– check header validity, – get data from calibration database

• pireduce (r)– remove crosstalk– subtract mean of overscan in each amp, trim– divide by gain for each amp– subtract bias, if specified– subtract dark, if specified– divide by flat, if specified

• pbias: run pireduce on bias frames, bias/ dark/ flat turned off• pflat (TBI) run pireduce on flat frames, dark/ flat turned off• pmosaic (m)

– combine amplifiers and ccd's into single fits files– can now be opened as normal image by DS9

• imcoadd (TBI)– remove distortion– combine mosaiced images, registering and removing cosmic rays

Spectroscopy• psreduce (ps)

– run pireduce – run pmosaic– using slitmask definition file (MDF), cut into one piece for each slit (pscut)– apply first guess wavelength calibration to each

• psflat (TBI) run psreduce on spectral flats (tungsten continuum spectrum)• pswavelength identify lines and update wavelength dispersion calibration for wavecal

frame• pstransform (TBI) resample cut spectra onto linear wavelength vs space grid• psskysub, psextract (TBI) extract to 1-d raw spectra• pscalibrate compute flux cal from flux standard

Configuration Data - CCD

Instrument configuration data: $salt/pfis/data (IRAF pfis$data)

• PFISamps gain and noise for ccd amps:# Database of PFIS CCD amplifier properties# 28 Oct 2005 - Lab Data# Note: Bias not updated - should depend on binning KHN# ROSPEED GAINSET GAIN RDNOISE BIAS AMPSLOW FAINT 1.19 2.46 2108 amp1SLOW FAINT 1.24 2.42 2064 amp2SLOW FAINT 1.30 2.33 2281 amp3SLOW FAINT 1.21 2.43 2285 amp4SLOW FAINT 1.20 2.91 2227 amp5SLOW FAINT 1.11 2.51 2241 amp6SLOW BRIGHT 2.91 3.74 2098 amp1SLOW BRIGHT 3.02 3.78 2097 amp2SLOW BRIGHT 3.15 3.62 2116 amp3SLOW BRIGHT 2.95 3.56 2104 amp4SLOW BRIGHT 3.03 4.14 2111 amp5SLOW BRIGHT 2.78 3.54 2101 amp6FAST FAINT 5.04 6.59 2224 amp1FAST FAINT 5.38 6.78 2164 amp2FAST FAINT 5.53 6.15 2200 amp3FAST FAINT 5.24 5.88 2179 amp4FAST FAINT 5.30 7.82 2162 amp5FAST FAINT 4.81 4.81 2161 amp6FAST BRIGHT 10.47 10.20 2123 amp1FAST BRIGHT 11.09 10.68 2098 amp2FAST BRIGHT 11.49 9.82 2115 amp3FAST BRIGHT 10.67 9.18 2104 amp4FAST BRIGHT 11.09 10.81 2098 amp5FAST BRIGHT 10.34 9.57 2095 amp6

• Commissioning: done

Configuration Data - Crosstalk

• PFISxtalk crosstalk coefficients:# PFIS CCD amplifier crosstalk data# from 20041201 gain = bright distortion image, outer amps duplicated# Date VCTM 2 2 4 3 6 5# SRC 1 2 3 4 5 62004-01-01 .001474 .001474 .001166 .001111 .001377 .001377

• Calibrated using line spectrum with bright lines across all 3 CCD’s• Package: MSCRED

– Calibration: XTCOEFF– Application: XTALKCOR (done in PIREDUCE)

• Commissioning: Needs redoing for all 4 gain/ speed combinations

Configuration Data - Mosaicing

• PFISgeom orientation of CCD's in mosaic:# PFIS CCD Geometry data# Date gap xshift(1) yshift(1) rot(1) xshift(3) yshift(3) rot(3)2004-01-01 90 -14.53 1.84 0.0931 2.35 0.84 -0.0337

– gap: nominal gap (columns) between ccd’s (unbinned pixels)– coordinate system: CCD 2– xshift: col shift (unbinned pixels) from nominal– yshift: row shift “– rotation: clockwise rotation of CCD (degrees)

• Recently updated using image of cartesian grid drilled by slitmask cutter. Can beupdated using residuals from dispersion curves of spectra

Configuration Data - Distortion

• PFISdistortion correct pincushion distortion of collimator

R/Rmax = r/rmax + A (r/rmax)3 + B (r/rmax)5

where Rmax, A and B are weak functions of wavelength:Rmax (8) = R0 + R18 + R2 / 82 + R3 / 83

A(8) = A0 + A1 / 8 + A2 / 82

B(8) = B0 + B1 / 8 + B2 / 826 of the 10 coefficients are also functions of temperature:

f(T) = f + ft (Th – T) / (Th –Tc) (Th =20; Tc=-5)

• Commissioning: needs to be rechecked using telescope calibration system

# PFIS Optical Distortion and Alignment Data# mm/4' Rm0 Rm1 Rm2 Rm3 Rm0t Rm2tRmax 27.6485 0.4246 0.0620 -0.0150 0.0165 -0.0012 ## norm@ 4' A0 A1 A2 A0t A1tCubic 0.013283 0.000296 -0.000273 0.000104 -0.000010## norm@ 4' B0 B1 B2 B0t B1tFifth 0.008488 -0.000716 0.000167 0.000095 -0.000024## pup dia P0 P1 P2Pupil 150.38638 -0.483418 0.184229# Alignment# Date dxd dyd rot dxc dyc# [pix] [pix] [arcmin] [pix] [pix]2004-01-01 -0.749 -13.776 -7.356 0.0 0.02005-06-01 8.572 -34.740 -8.691 -34.647 15.043

Configuration Data - Gratings• PFISgratings. grating list with alignment calibration

# PFIS Gratings 23 March, 2005# (Super)Blaze Simul Wavel Alignment# Grating Ruling wavel R coverage interval Rot Tip# [id] [lines/mm] [nm] [nm] [nm] ['] [']PG0300 300 520 350 500 380 1050 2.59 0 PG0900 902.30 634 1330 308 320 1050 0.03 -2.99PG1300 1299.61 500 1550 210 350 1050 0.75 1.12PG1800 1801.28 624 3030 133 400 930 0.75 2.07PG2300 2301.36 480 3000 105 320 730 0.35 0.82PG3000 2999.98 366 2800 81 320 560 -0.95 1.68## Articulation Station Error (pixels)# Station Xerr Yerr# [deg] [pix] [pix]1.75 10.2 -0.732.50 10.2 -1.053.25 10.2 -1.364.00 10.2 -1.674.75 10.2 -1.985.50 10.2 -2.29

• Commissioning: Articulation Station error needs to be calibrated, all stations

• /linelists. linelists for calibration lamps: Xe, Ne, HgAr– Commissioning: these need to be culled

• PFISfilters. filter list with pointers to transmission curves in /filters• /masks. mask definition files: Subject for next time!

Astronomy 920Commissioning of the Robert Stobie Prime Focus Imaging Spectrograph

Meeting 9Slitmask Planning

• Get catalogue with good astrometry• Define target priority• Get image• Optimize Field center, roll• Iterate till you like it• Generate output files

Slitmask Input Catalogue• Import (J2000) astrometry, properties (I use EXCEL)

– Positions good to slitsize/5, at least– Best to use purpose astrometry from literature (usually published as catalogues inSimbad)– Define your priorities

• Make prioritized ascii slitmask catalog:

ID RA(deg) Dec(deg) Pri1034 274.66183 -13.77889 111600 274.79617 -13.94525 101090 274.67313 -13.81108 81164 274.68771 -13.76125 8926 274.63667 -13.75308 81064 274.66704 -13.75514 81168 274.68863 -13.78886 8

Slitmask Optimization/ Output

• Run Optimizer, display– typical max number of spectra 25 - 30– place largest possible number of high priority targets on N slitmasks– grid of RA, Dec, Roll

• Iterate catalogue, reference stars, priorities to get desired objects into n slitmasks• Create G-Code (laser-cutter .nc) and IRAF (.mdf) files, included with Phase II

proposal

Output FilesG-Code (.nc):

G71M102M104KN310KN320M3M98G90 X65Y60M98KN330V1=11.7298V2=-16.623V3=0......

Assignment for next Time

• Plan a SALT MOS Project: Grating Spectroscopy of cluster of stars orGalaxies– One page writeup of why it is scientifically interesting– Use PFIS PI Tool to verify S/N and produce XML configuration definition file: – Plan a slitmask: .psm file

• Next Meeting: 18 Nov (no meeting next week: SALT inauguration)


Meeting 10Longslit Spectroscopy

• Data Format• Acquisition• Wavelength calibration

Slitviewer• Long Slits:

– polished metal– tilted

• Light not going through slit relayed to acquisition camera• Use

– peak-up position– verify target– document

Wavelength Calibration• Calibration system

– red, blue light guides– Ne, Xe, HgAr, ThAr, CuAr line lamps– QTH (Quartz Tungsten Halogen) continuum with color balance filters

For Next Time (Dec 2)• Data to play with, on class website

– Imaging, 20051030• 1-5 Biases• 16 47 Tuc, 629 nm filter

– Spectroscopy, 20051106• 30: Ne Lamp• 31: Xe Lamp• 35-37 Biases• 38, 39 10, 60 sec on BD -07 281• Exercise #2

– pbias biases– pireduce, pmosaic 47 Tuc, Ne, Xe, BD -7 281– extra credit: extract spectrum, wavelength calibrate


Meeting 11Polarimetry: Beamsplitter; data formats

Polarimetric OpticsPolarizing Beamsplitter

• In Collimated beam, just before camera• Mosaic of 9 Calcite “Wollaston” Prisms• Splitting 4.8 – 5.8 deg (color dependent): 240 – 280 arcsec at CCD

Grating Spectropolarimetry• Setup

– Tungsten Continuum– Test slitmask masked to center 4’– Polaroid screwed to slitmask

• Polarization signal = (E-O)/(E+O)

• Dual Beam cancels out transparency changes

Imaging SpectroPolarimetry• Setup

– HgAr Arc Lamp– Clear Filter (320 – 1000 nm)– Pinhole slitmask masked to central 4’

• Entire PFIS accessible spectrum spread out into 25 arcsec mini-spectrum bychromatic dependence of beamsplitter

• Low resolution spectropolarimetry of all stars in field

Fabry-Perot Spectropolarimetry• Setup

– LR FP tuned to Ne line 6506.5– Polaroid

• Data product: FP scan => data cube of line polarization profile• Never before tried


Meeting 12Polarimetry: Waveplate Modulation; Calibration

Modulating the Signal with Waveplates

• 1/2 and 1/4 wave retardation plates– switch which beam has which sense of polarization to remove response variationswith time by rotating plate – remove polarization sensitivity of optical elements after waveplates– measure different Stokes parameters:

• (Q,U): linear; V: circular– Q/I = (I(y) – I(x)) / (I(y) + I(x)) (measured directly by beamsplitter)– U/I = (I(+45) – I(-45)) / (I(+45) + I(-45))– V/I = (I(rcp) – I(lcp)) / (I(rcp + I(lcp)

Waveplate Optics• Pancharatnam “superachromatic” waveplates

– at beginning of collimator– sandwich of 6 very thin pieces of crystal quartz and magnesium fluoride(birefringent materials)– 320 nm – 1.7 microns to accommodate visible and NIR beams

• 1/2 wave: 100 mm diameter (full field• 1/4 wave: 60 mm diameter (3 arcmin field)

Dual-Beam Polarimeter Basics• Signal:

f = [ I’’(E) – I’’(O) ] / [ I’’(E) + I’’(O) ]= Q’ / I’= 1/2 (1-cos J) (Q/I cos 4R + U/I sin 4R) + sin J V/I sin 2R

• Linear pol (Q,U) modulated 100% at 4R by J = 1/2 8 waveplate• Circular pol (V) modulated 100% at 2R by J = 1/4 8 waveplate

PFIS waveplate patterns• 1/2 waveplate followed optionally by 1/4 waveplate

Linear Circular All-Stokes1/2 8 1/4 8 1/2 8 1/4 8 1/2 8 1/4 80 0 0 +45 0 045 0 0 -45 22.5 33.7522.5 0 22.5 -45 45 67.567.5 0 22.5 +45 67.5 101.2511.25 0 45 +45 90 13556.25 0 45 -45 112.5 168.7533.75 0 67.5 -45 135 202.578.75 0 67.5 +45 147.5 236.25

Halfwave Efficiency• Efficiency = (1 – cos J ) / 2• Measure efficiency with polaroid at slitmask• Absolute axis angle measured with stars of known polarization

Quarterwave Efficiency• Predicted efficiency = sin J • Measure with polaroid + 1/4 waveplate at slitmask

Instrumental Polarization• Linear instrumental: from non-normal reflections off mirrors + net asymmetry due to

– off-axis in FOV– asymmetric illumination of mirror at ends of track

• Predict from ray-trace < ~ 0.1% (typical)• Measure with known unpolarized stars •

Commissioning Status• Ready, limited by telescope: Imaging, Long Slit• Not ready, with my guesses

– Fabry-Perot: March– MOS: April– Polarimetry: May

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Astronomy 920 Commissioning of the Prime Focus Imaging ...khn/ast920/Astronomy 920.pdf · Astronomy 920 Commissioning of the Prime Focus Imaging Spectrograph Meeting 1 Organization;