# Presentation: 265851

## Spectrograph calibration

- Determination of specifications
- Calibration strategy

- Note in http://www.astrsp-mrs/snap/spectro/calib-spectro.ps

## 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

## 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 %:

## 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 |
| redshift |  | 25 |

## Calibration strategy

- 3 steps:
- Optical distortion measurement and corrections
- Wavelength calibration
- Flux calibration

## 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

## 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

## 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

## 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