Synthesizing Sun-as-a-star flare spectra from high-resolution solar observations

TL;DR

This paper develops a method to generate synthetic Sun-as-a-star spectra from high-resolution solar flare observations, enabling better interpretation of stellar observations by accounting for spatial and rotational effects.

Contribution

It introduces the NESSI code to produce realistic full-disk spectra from small solar observations, bridging the gap between solar and stellar spectral analysis.

Findings

Synthetic spectra reveal limitations in inferring solar processes from Sun-as-a-star data.

The method accounts for center-to-limb variations and differential rotation effects.

Results improve interpretation of stellar flare observations using solar data.

Abstract

Spatially resolved observations of the Sun and the astronomical sample size of stellar bodies are the respective key strengths of solar and stellar observations. However, the large difference in object brightness between the Sun and other stars has led to distinctly different instrumentation and methodologies between the two fields. We produce and analyze synthetic full-disk spectra derived from 19 small area field-of-view optical observations of solar flares acquired by the Swedish 1-m Solar Telescope (SST) between 2011 and 2024. These are used to investigate what can and cannot be inferred about physical processes on the Sun from Sun-as-a-star observations. The recently released Numerical Empirical Sun-as-a-Star Integrator (NESSI) code provides synthetic full-disk integrated spectral line emission based on smaller field-of-view input, accounting for center-to-limb variations and differential rotation. We use this code to generate pseudo-Sun-as-a-star spectra from the SST observations. ...