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Advanced Physical Modeling of Instruments in ESO’s Instrumentation Division

This document explores the physical modeling approaches employed by the European Southern Observatory (ESO) in their Instrumentation Division. It covers various aspects, including instrument modeling concepts and details, optical design utilizing Zemax software, and the importance of collaboration with partners like NASA and NIST. The text emphasizes the techniques used for testing, commissioning, and calibrating instruments like CRIRES and STIS. A focus is placed on predictive calibration strategies and the integration of input data for enhanced scientific outcomes.

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Advanced Physical Modeling of Instruments in ESO’s Instrumentation Division

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  1. Physical Modelling of Instruments Activities in ESO’s Instrumentation Division Florian Kerber, Paul Bristow

  2. 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) • J. Reader, G. Nave, C.J. Sansonetti • CHARMS (NASA, Goddard SFC) • D.B. Leviton, B.J. Frey

  3. Outline • Instrument Modelling - Concept • Instrument Modelling - Basics • Instrument Modelling - Details • Input for the Model • Discussion

  4. 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

  5. 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

  6. Physical Model • Optical Model (Ray trace) • High quality Input Data • Simulated Data • Close loop between Model and Observations • Optimizer Tool (Simulated Annealing)

  7. 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 # of lines: Pt-Ne 258 vs Pt/Cr-Ne 1612

  8. STIS

  9. STIS Science Demo Case: Result 10-4 nm 1 pixel Standard:=(3.3 ± 1.9) STIS Model:=(0.6 ± 1.7)

  10. 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

  11. Physical Model Approach • Essentially same input as the polynomial: • x,y location on detector • Entrance slit position (ps) & wavelength () • Require that the model maps: for all observed features.

  12. 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

  13. Model Kernel

  14. 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

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

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

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

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

  19. Simulated Stellar Spectrum

  20. 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

  21. Near IR Wavelength Standards 1270–1290 nm Ne Kr Th-Ar

  22. 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)

  23. Measurements with FTS at ESO

  24. Spectrum - Operating Current

  25. 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

  26. CRIRES pre-disperser prism - ZnSe n(,T) from CHARMS, (GSFC, NASA) Leviton & Frey, 2004

  27. ZnSe Prism: Temperature 73 - 77 K • Measured line shifts • Physical Model • Th-Ar line list • n(,T) & dn/dT of ZnSe 1124 1138 Wavelength [nm]

  28. Location of Th-Ar lines - Temperature

  29. 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!

  30. 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

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