Simulations of instrumental effects on spectropolarimetric solar observations for the VTF
Simulated maps of a solar region. The panels show a comparison of the full-width-half-maximum values (left) and Doppler velocities (right) for two different instrument setups (1: middle row, three FPIs; 2: bottom row, two FPIs). The panels on the left and top right show the ideal case without errors. The bottom right panels display the resulting maps with induced errors for both instruments.
A measurement of a Quiet Sun region was simulated with and without instrumental defects. For a tele-centric setup of the interferometers in the optical path (like planned for the VTF), the detection of flatness defects of the surfaces is of crucial importance.
The figure shows the impact of lokal defects of the plate spacing of Fabry-Pérot interferometers on an observation of a granular region on the Sun. The differences for two instrumental configurations become apparent between a Triple-FPI system (instrument 1, middle row) with a high spectral resolution of 200,000 and a Tandem-FPI system (instrument 2, bottom row) with a resolution of 200,000 at a central wavelength of 630.25nm.
To clarify the differences, the panels showing the ideal full-width-half-maximum values (left) are compared with the results including the simulated instrumental impacts of statistically distributed local plate defects with a root mean square of 2.5nm. The obtained Doppler velocities of the ideal case without defects (upper right) and including the flatness errors for both instruments (lower right) emphasize the differences and the relevance of this study.
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