Physical Modelling of Instruments

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Physical Modelling of Instruments. Activities in ESOs Instrumentation Division. Florian Kerber, Paul Bristow. Our Partners. INS, TEC, DMD, LPO, Instrument Teams (CRIRES, X-shooter ) Space Telescope European Coordinating Facility (ST-ECF) M.R. Rosa Atomic Spectroscopy Group (NIST) - PowerPoint PPT Presentation


  • Physical Modelling of Instruments Activities in ESOs Instrumentation DivisionFlorian Kerber, Paul Bristow

  • Our PartnersINS, TEC, DMD, LPO, Instrument Teams (CRIRES, X-shooter )Space Telescope European Coordinating Facility (ST-ECF)M.R. RosaAtomic Spectroscopy Group (NIST)J. Reader, G. Nave, C.J. SansonettiCHARMS (NASA, Goddard SFC)D.B. Leviton, B.J. Frey

  • OutlineInstrument Modelling - ConceptInstrument Modelling - BasicsInstrument Modelling - Details Input for the ModelDiscussion

  • Building & Operating an InstrumentScience RequirementsOptical Design (code V, Zemax) Engineering ExpertiseTesting and Commissioning

    Operation and Data FlowCalibration of InstrumentScientific Data and Archive

  • From Concept to ApplicationM. Rosa: Predictive calibration strategies: The FOS as a case study (1995)P. Ballester, M. Rosa: Modeling echelle spectrographs (A&AS 126, 563, 1997) P. Ballester, M. Rosa: Instrument Modelling in Observational Astronomy (ADASS XIII, 2004) Bristow, Kerber, Rosa: four papers in HST Calibration Workshop, 2006UVES, SINFONI, FOS, STIS, VLTI, ETC

  • Physical ModelOptical Model (Ray trace)High quality Input DataSimulated DataClose loop between Model and ObservationsOptimizer Tool (Simulated Annealing)

  • STIS-CE Lamp Project Pt-Ne atlas, Reader et al. (1990) done for GHRSSTIS uses Pt/Cr-Ne lampImpact of the Cr lines strongest in the NUV List of > 5000 lines accurate to < 1/1000 nm

    Echelle, c 251.3 nm # of lines: Pt-Ne 258 # of lines: Pt-Ne 258 vs Pt/Cr-Ne 1612

  • STIS

  • Standard: =(3.3 1.9)STIS Model: =(0.6 1.7)STIS Science Demo Case: Result 1 pixel10-4 nm

  • Traditional Wavelength CalibrationData collected for known wavelength source (lamp or sky):Match observed features to wavelengths of known featuresFit detector location against wavelength => polynomial dispersion solution

  • Physical Model ApproachEssentially same input as the polynomial:x,y location on detectorEntrance slit position (ps) & wavelength ()Require that the model maps: for all observed features.

  • CRIRES950 - 5000 nmResolution / 100,000ZnSe pre-disperser prismEchelle 31.6 lines/mm4 x Aladdin III 1k x1k InSb arrayCommissioning June 06

  • Model Kernel

  • Model KernelSpeedStreamlined (simplistic) descriptionFast - suitable for multiple realisationsSpectrograph (CRIRES - cold part only)Tips and tilts of principal componentsDispersive behaviour of prism and gratingDetector layoutThis is not a full optical model

  • Operating Modes (foreseen)General optimisation (calibration scientist, offline)Grating & prism optimisation (automatic)Data reduction (pipeline)Data simulation (interactive, offline)

  • Operating Modes (foreseen)General optimisation (calibration scientist, offline)Grating & prism optimisation (automatic)Data reduction (pipeline)Data simulation (interactive, offline)

  • Operating Modes (foreseen)General optimisation (calibration scientist, offline)Grating & prism optimisation (automatic)Data reduction (pipeline)Data simulation (interactive, offline)

  • Operating Modes (foreseen)General optimisation (calibration scientist, offline)Grating & prism optimisation (automatic)Data reduction (pipeline)Data simulation (interactive, offline)

  • Simulated Stellar Spectrum

  • Optimisation StrategyTake limits from design and constructionOne order/mode - rich spectraOptimise detector layoutMultiple order/modes (detector layout fixed)Optimise all except prism/gratingAll order/modes (all parameters fixed except prism/grating)Optimise prism/grating settings for each mode

  • Near IR Wavelength Standards12701290 nmTh-ArNeKr

  • Th-Ar lamp:Visible and Near IREstablished standard source in VisualPalmer & Engleman (1983) 278 - 1000 nmFEROS, FLAMES, HARPS, UVES, Xshooter Cryogenic High Resolution Echelle Spectrometer (CRIRES) at VLT950 - 5000 nm, Resolution ~100,000Project to establish wavelength standards (NIST)UV/VIS/IR 2 m Fourier Transform Spectrometer (FTS)

  • Measurements with FTS at ESO

  • Spectrum - Operating Current

  • Th-Ar in the near IR: Summary> 2000 lines as wavelength standards in the range 900 - 4500 nm

    insight into the properties of Th-Ar lamps, variation of the spectral output/continuum as a function of current

    Th-Ar hollow cathode lamps - a standard source for wavelength calibration for near IR astronomy

  • CRIRES pre-disperser prism - ZnSen(,T)

    from CHARMS, (GSFC, NASA)Leviton & Frey, 2004

  • ZnSe Prism: Temperature 73 - 77 KMeasured line shiftsPhysical ModelTh-Ar line listn(,T) & dn/dT of ZnSeWavelength [nm]11241138

  • Location of Th-Ar lines - Temperature

  • Conclusions - Physical ModelPreserve know how about instrumentReplace empirical wavelength calibration High quality input data is essentialPredictive powerSupport instrument developmentassess expected performancereduce riskCalibration data is still required!

  • Conclusions - Physical ModelThe resulting calibration is predictive and expected to be more preciseThe process of optimising the model is somewhat more complex than fitting a polynomialUnderstanding of physical properties and their changesCRIRES will be the first ESO instrument to utilise this approach to calibration


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