Stray light correction and contrast analysis of Hinode broad band images

TL;DR

This paper models and corrects for stray light in Hinode broad band solar images using Mercury transit data, leading to improved contrast measurements of solar features across different wavelengths.

Contribution

It introduces a method to accurately model and deconvolve instrumental scattered light in Hinode images, enhancing the contrast analysis of solar features.

Findings

Corrected images show increased contrast of solar features.

Contrast values are wavelength-dependent, with higher contrasts at shorter wavelengths.

Bright point contrast is higher in the CN-band than in the G-band, confirming theoretical predictions.

Abstract

The contrasts of features in the quiet Sun are studied using filtergrams recorded by the Broad-band Filter Imager on the Hinode/Solar Optical Telescope. In a first step, the scattered light originating in the instrument is modeled using Mercury transit data. Combinations of four two-dimensional Gaussians with different widths and weights were employed to retrieve the point-spread functions (PSF) of the instrument at different wavelengths, which also describe instrumental scattered light. The parameters of PSFs at different wavelengths are tabulated. The observed images were then deconvolved using the PSFs. The corrected images were used to obtain contrasts of features such as bright points and granulation in different wavelength bands. After correction, rms contrasts of the granulation of between 0.11 (at 668 nm) and 0.22 (at 388 nm) are obtained. Similarly, bright point contrasts ranging from 0.07 (at 668 nm) to 0.78 (at 388 nm) are found, which are a factor of 1.8 to 2.8 higher than those obtained before PSF deconvolution. The mean contrast of the bright points is found to be somewhat higher in the CN-band than in the G-band, which confirms theoretical predictions.