1. A. Ealet Berkeley, december 2002 1 1 Spectrograph calibration Determination of specifications Calibration strategy Note in http://www.astrsp-mrs/snap/spectro/calib-spectro.ps

2. A. Ealet Berkeley, december 2002 2 2 Effect on physics Any systematic effect causing a dependence in redshift of the flux will affect the budget error. As example a linear effect as  =  (1+az) will imply: to control cosmological parameters at 2 % need a slope a< 2 % to control w’ at 10 %, need a slope a< 2 % Calibration error can go inside this systematic budget error if: spectra are used to reduce systematic with corrections there is a dependence along the wavelength range in flux or in wavelength Statistical error will not affect so much the error budget Overall scale error would have NO IMPACT and will not be considered

3. A. Ealet Berkeley, december 2002 3 3 Specifications Si line measurement for velocity/temperature measurement Evaluate Si line position drift on the  range Disentangle dust evaluation and metallicity effect Evaluate the relative flux variation on the range Spectrophotometric calibration for cross check or filter monitoring Not affected by a linear dependence, control on quadratic variation Redshift measurement if done is affected by the same error type evaluate wavelength variation Evaluations of a dependence along the full wavelength to control an effect at 2 %:

4. A. Ealet Berkeley, december 2002 4 4 SUMMARY goal flux Wavelength (A°) Si line position 20 Dust measurement 5 10 -2 Magnitude/filter monitoring Flat field Wavelength 5 10 -2 2 10 -2 70 redshift25

5. A. Ealet Berkeley, december 2002 5 5 Calibration strategy 3 steps: Optical distortion measurement and corrections Wavelength calibration Flux calibration

6. A. Ealet Berkeley, december 2002 6 6 Distortion measurement spatial spectral Iso Adjust parameterization of the detector plan with optical simulation Precise mapping on ground with monochromatic point source Verify after launch and correct if needed Not expected to change in time

7. A. Ealet Berkeley, december 2002 7 7 Wavelength and flux calibration Wavelength calibration Need lamp covering the full wavelength range with lines Expected precision with spectral dithering is 20 A at  = 1.7  m To be done after launch to correct mapping if needed not expected to change a lot, monitoring only Flux calibration Flat field extended lamp as the imager one with broad spectrum variation of gain can be control at 1 %. Absolute calibration Needed to correct residual effects and the wavelength dependence at 2 % Use calibrated stars with calibrated spectra Need shutter for short exposure time Periodicity can follow the imager one PSF calibration stars with narrow lines Slit effect correction need spatial dithering

8. A. Ealet Berkeley, december 2002 8 8 Future plan and studies Detailed simulation development will provide: Optic studies: detector mapping, distortion corrections, PSF shape and size, quantification of dithering Detector studies: noise and dark current effects, gain variations, inhomogeneity estimation Spectral sources simulation : simulate broad or line sources for calibration procedure Long term : Put the complete Calibration procedure in the full simulation to evaluate impact on physics

9. A. Ealet Berkeley, december 2002 9 9 Requirements Extended lamp similar to imager source for flat fielding Lamps with lines which cover the full wavelength range (Can be also the imager lamp) Calibrated stars with calibrated spectra at 2 % in flux Shutter for short exposure time of bright stars ( 2%) (or use the imager shutter..) Spatial dithering for slit effect Spectral dithering possible for wavelength calibration