Sun-as-a-star Analyses of Various Solar Active Events Using H$\alpha$ Spectral Images Taken by SMART/SDDI

TL;DR

This study analyzes Sun-as-a-star Hα spectral data of various solar active events to understand their spectral features and implications for stellar observations, revealing distinct signatures for different phenomena and their potential to produce CMEs.

Contribution

It introduces a comprehensive Sun-as-a-star analysis of diverse solar active events using Hα spectra, highlighting spectral signatures and their relation to stellar activity interpretation.

Findings

Sun-as-a-star spectra show emission changes of order 10^{-4} Å.

Different active events exhibit distinct spectral features, such as line center emission and Doppler shifts.

Filament eruptions, even with red-shifted absorption, can lead to CMEs.

Abstract

Sun-as-a-star analyses, in which observational data is spatially integrated, are useful for interpreting stellar data. For future applications to stellar observations, we performed Sun-as-a-star analyses of H$\alpha$ spectra for various active events on the Sun, not only for flares and filament eruptions/surges on the solar disk, but also for eruptions of off limb prominences using H$\alpha$ spectral images taken by the Solar Magnetic Activity Research Telescope / Solar Dynamics Doppler Imager (SMART/SDDI) at Hida Observatory, Kyoto University. All the analyzed events show emission relative to the pre-event state and the changes in their H$\alpha$ equivalent widths are all on the orders of 10$^{-4}$ \r{A}. Sun-as-a-star H$\alpha$ spectra exhibit different features depending on the causes of the emission: (i) Flares show emission at the H$\alpha$ line center, together with red asymmetry and line broadening, as reported in a previous study. (ii) Filament eruptions with and without flares show emission near the H$\alpha$ line center, accompanied by blue-/red-shifted absorption. Notably, disappearance of dark filaments leads to the apparent enhancement of the H$\alpha$ line center emission. (iii) Eruptions of off limb prominences show blue-/red-shifted emission. These spectral features enable us to identify the active phenomena on Sun-like stars. We have also found that even the filament eruptions showing red-shifted absorptions in Sun-as-a-star H$\alpha$ spectra lead to coronal mass ejections (CMEs). This result suggests that even if the falling components of stellar filament eruptions are detected as red-shifted absorptions in H$\alpha$ spectra, such stellar filament eruptions may also develop into CMEs.