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

2. 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. 3 Outline  Instrument Modelling - Concept  Instrument Modelling - Basics  Instrument Modelling - Details  Input for the Model  Discussion

4. 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. 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. 6 Physical Model  Optical Model (Ray trace)  High quality Input Data  Simulated Data  Close loop between Model and Observations  Optimizer Tool (Simulated Annealing)

7. 7 STIS-CE Lamp Project  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 Echelle, c  251.3 nm # of lines: Pt-Ne 258# of lines: Pt-Ne 258 vs Pt/Cr-Ne 1612

8. 8 STIS

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

10. 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. 11 Physical Model Approach  Essentially same input as the polynomial: –x,y location on detector –Entrance slit position (p s ) & wavelength ( )  Require that the model maps: for all observed features.

12. 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. 13 Model Kernel

14. 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. 15 Operating Modes (foreseen) 1. General optimisation (calibration scientist, offline) 2. Grating & prism optimisation (automatic) 3. Data reduction (pipeline) 4. Data simulation (interactive, offline)

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17. 17 Operating Modes (foreseen) 1. General optimisation (calibration scientist, offline) 2. Grating & prism optimisation (automatic) 3. Data reduction (pipeline) 4. Data simulation (interactive, offline)

18. 18 Operating Modes (foreseen) 1. General optimisation (calibration scientist, offline) 2. Grating & prism optimisation (automatic) 3. Data reduction (pipeline) 4. Data simulation (interactive, offline)

19. 19 Operating Modes (foreseen) 1. General optimisation (calibration scientist, offline) 2. Grating & prism optimisation (automatic) 3. Data reduction (pipeline) 4. Data simulation (interactive, offline)

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21. 21 Simulated Stellar Spectrum

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23. 23 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

24. 24 Near IR Wavelength Standards 1270–1290 nm Th-Ar Ne Kr

25. 25 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)

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27. 27 Measurements with FTS at ESO

28. 28 Spectrum - Operating Current

29. 29 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

30. 30 CRIRES pre-disperser prism - ZnSe n(,T) from CHARMS, (GSFC, NASA) Leviton & Frey, 2004

31. 31 Wavelength [nm] 11241138  Measured line shifts  Physical Model –Th-Ar line list –n(,T) & dn/dT of ZnSe ZnSe Prism: Temperature 73 - 77 K

32. 32 Location of Th-Ar lines - Temperature

33. 33 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!

34. 34 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