Precise Reduction of Solar Spectra Observed by the 1-meter New Vacuum Solar Telescope

TL;DR

This paper introduces a highly precise spectral data reduction procedure for the NVST, improving measurement accuracy of solar Doppler velocities and enabling detailed co-temporal, co-spatial solar atmospheric studies.

Contribution

The paper presents a novel comprehensive reduction method that corrects geometric distortions and flat-field errors, achieving higher accuracy in solar spectral measurements.

Findings

Doppler velocity measurement accuracy within 100 ms-1

Enhanced ability to study photosphere and chromosphere simultaneously

Effective correction of spectral line drifts and intensity fluctuations

Abstract

We present a precise and complete procedure for processing spectral data observed by the 1-meter New Vacuum Solar Telescope (NVST). The procedure is suitable for both the sit-and-stare and raster-scan spectra. In this work, the geometric distortions of the spectra are firstly corrected for subsequent processes. Then, considering the temporal changes and the remnants of spectral lines in the flat-field, the original flat-field matrix is split into four independent components for ensuring a high precision flat-fielding correction, consisting of the continuum gradient matrix, slit non-uniform matrix, CCD dust matrix, and interference fringe matrix. Subsequently, the spectral line drifts and intensity fluctuations of the science data are further corrected. After precise reduction with this procedure, the measuring accuracies of the Doppler velocities for different spectral lines and of the oscillation curves of the chromosphere and photosphere are measured. The results show that the highest measuring accuracy of the Doppler velocity is within 100 ms-1, which indicates that the characteristics of the photosphere and chromosphere can be studied co-spatially and co-temporally with the reduced spectra of NVST.