Correction of atmospheric stray-light in restored slit-spectra

TL;DR

This paper presents a statistical method to correct residual atmospheric stray-light contamination in ground-based solar slit spectra, improving data quality and revealing more accurate solar granulation velocities.

Contribution

It introduces a novel application of statistical stray-light correction to slit spectra, enhancing the accuracy of solar observations from ground-based telescopes.

Findings

Increased RMS granulation contrast to 12.5%.

Spectral lines become deeper in granules and shallower in intergranular lanes.

Higher observed velocities of solar granulation.

Abstract

A long-standing issue in solar ground-based observations has been the contamination of data due to stray light, which is particularly relevant in inversions of spectropolarimetric data. We aim to build on a statistical method of correcting stray-light contamination due to residual high-order aberrations and apply it to ground-based slit spectra. The observations were obtained at the Swedish Solar Telescope, and restored using the multi-frame blind deconvolution restoration procedure. Using the statistical properties of seeing, we created artificially degraded synthetic images generated from magneto-hydrodynamic simulations. We then compared the synthetic data with the observations to derive estimates of the amount of the residual stray light in the observations. In the final step, the slit spectra were deconvolved with a stray-light point spread function to remove the residual stray light from the observations. The RMS granulation contrasts of the deconvolved spectra were found to increase to approximately 12.5%, from 9%. Spectral lines, on average, were found to become deeper in the granules and shallower in the inter-granular lanes, indicating systematic changes to gradients in temperature. The deconvolution was also found to increase the redshifts and blueshifts of spectral lines, suggesting that the velocities of granulation in the solar photosphere are higher than had previously been observed.