Wavelength errors in spectrographs. I: the effect of surface irregularities in camera mirrors.
Applied Optics
|January 15, 2010
Summary
Camera mirror imperfections in high-dispersion astronomical spectrographs reduce radial velocity precision. Zonal irregularities cause variable spectral shifts, impacting accuracy, especially with larger gratings.
Area of Science:
- Astronomy
- Optical Engineering
Background:
- High-dispersion astronomical spectrographs often yield lower radial velocity precision than theoretically expected.
- This discrepancy is partly attributed to optical aberrations within the instrument's camera mirror.
Purpose of the Study:
- To investigate the impact of camera mirror zonal imperfections on radial velocity precision in astronomical spectrographs.
- To quantify the relationship between mirror surface irregularities and measurement errors.
Main Methods:
- Analytical modeling of spectral shifts caused by sinusoidal zonal irregularities in a camera mirror.
- Calculation of the standard deviation in radial velocity as a function of mirror properties and instrument parameters.
Main Results:
- Variable spectral shifts along the spectrograph plate, caused by mirror imperfections, directly affect radial velocity precision.
- The standard deviation in radial velocity is inversely proportional to angular dispersion and the size of the dispersing element (grating/prism).
- A specific example shows a 0.06 km/sec standard deviation for a 300-mm grating with 1/20 wavelength surface fluctuation.
Conclusions:
- Zonal imperfections in camera mirrors are a significant source of error in high-dispersion astronomical radial velocity measurements.
- Optimizing mirror surface quality and instrument design (dispersion, size) is crucial for achieving higher precision in astronomical observations.
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