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Physical Modelling of Instruments Activities in ESO’s Instrumentation Division Florian Kerber, Paul Bristow Our Partners INS, TEC, DMD, LPO, … Instrument Teams (CRIRES, X-shooter …) Space Telescope European Coordinating Facility (STECF) – Atomic Spectroscopy Group (NIST) – M.R. Rosa J. Reader, G. Nave, C.J. Sansonetti CHARMS (NASA, Goddard SFC) – D.B. Leviton, B.J. Frey 2 Outline Instrument Modelling - Concept Instrument Modelling - Basics Instrument Modelling - Details Input for the Model Discussion 3 Building & Operating an Instrument Science Requirements Optical Design (code V, Zemax) Engineering Expertise Testing and Commissioning Operation and Data Flow Calibration of Instrument Scientific Data and Archive 4 From Concept to Application M. 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, 2006 UVES, SINFONI, FOS, STIS, VLTI, ETC 5 Physical Model Optical Model (Ray trace) High quality Input Data Simulated Data Close loop between Model and Observations Optimizer Tool (Simulated Annealing) 6 STIS-CE Lamp Project Echelle, c 251.3 nm Pt-Ne atlas, Reader et al. (1990) done for GHRS STIS uses Pt/Cr-Ne lamp Impact of the Cr lines strongest in the NUV List of > 5000 lines accurate to < 1/1000 nm # of lines: Pt-Ne 258 vs Pt/Cr-Ne 7 1612 STIS 8 STIS Science Demo Case: Result 10-4 nm 1 pixel Standard: =(3.3 ± 1.9) STIS Model: =(0.6 ± 1.7)9 Traditional Wavelength Calibration Data collected for known wavelength source (lamp or sky): – Match observed features to wavelengths of known features – Fit detector location against wavelength => polynomial dispersion solution 10 Physical Model Approach Essentially same input as the polynomial: – x,y location on detector – Entrance slit position (ps) & wavelength () Require that the model maps: ps, x, y for all observed features. 11 CRIRES 950 - 5000 nm Resolution / 100,000 ZnSe pre-disperser prism Echelle 31.6 lines/mm 4 x Aladdin III 1k x1k InSb array Commissioning June 06 12 Model Kernel 13 Model Kernel Speed – Streamlined (simplistic) description – Fast - suitable for multiple realisations Spectrograph (CRIRES - cold part only) – Tips and tilts of principal components – Dispersive behaviour of prism and grating – Detector layout This is not a full optical model 14 Operating Modes (foreseen) 1. 2. 3. 4. General optimisation (calibration scientist, offline) Grating & prism optimisation (automatic) Data reduction (pipeline) Data simulation (interactive, offline) 15 16 Operating Modes (foreseen) 1. 2. 3. 4. General optimisation (calibration scientist, offline) Grating & prism optimisation (automatic) Data reduction (pipeline) Data simulation (interactive, offline) 17 Operating Modes (foreseen) 1. 2. 3. 4. General optimisation (calibration scientist, offline) Grating & prism optimisation (automatic) Data reduction (pipeline) Data simulation (interactive, offline) 18 Operating Modes (foreseen) 1. 2. 3. 4. General optimisation (calibration scientist, offline) Grating & prism optimisation (automatic) Data reduction (pipeline) Data simulation (interactive, offline) 19 20 Simulated Stellar Spectrum 21 22 Optimisation Strategy Take limits from design and construction One order/mode - rich spectra – Optimise detector layout Multiple order/modes (detector layout fixed) – Optimise all except prism/grating All order/modes (all parameters fixed except prism/grating) – Optimise prism/grating settings for each mode 23 Near IR Wavelength Standards 1270–1290 nm Ne Kr Th-Ar 24 Th-Ar lamp:Visible and Near IR Established standard source in Visual – Palmer & Engleman (1983) 278 - 1000 nm – FEROS, FLAMES, HARPS, UVES, Xshooter Cryogenic High Resolution Echelle Spectrometer (CRIRES) at VLT – 950 - 5000 nm, Resolution ~100,000 – Project to establish wavelength standards (NIST) – UV/VIS/IR 2 m Fourier Transform Spectrometer (FTS) 25 26 Measurements with FTS at ESO 27 Intensity [normalised to 10 mA] Spectrum - Operating Current 8 7 6 5 4 Argon Thorium 3 2 1 0 2 6 10 14 18 22 Lamp operating current [mA] 28 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 29 CRIRES pre-disperser prism - ZnSe n(,T) from CHARMS, (GSFC, NASA) Leviton & Frey, 2004 30 ZnSe Prism: Temperature 73 - 77 K Measured line shifts Physical Model – Th-Ar line list – n(,T) & dn/dT of ZnSe 1124 Wavelength [nm] 1138 31 Location of Th-Ar lines - Temperature 5 4,5 4 Shift [pixel] 3,5 3 1124 1138 1124 1138 2,5 2 nm nm nm pred nm pred 1,5 1 0,5 0 72,5 73,5 74,5 75,5 Temperature [K] 76,5 77,5 78,5 32 Conclusions - Physical Model Preserve know how about instrument Replace empirical wavelength calibration High quality input data is essential Predictive power Support instrument development – assess expected performance – reduce risk Calibration data is still required! 33 Conclusions - Physical Model The resulting calibration is predictive and expected to be more precise The process of optimising the model is somewhat more complex than fitting a polynomial Understanding of physical properties and their changes CRIRES will be the first ESO instrument to utilise this approach to calibration 34