Sun-as-a-star Analyses of Various Solar Active Events Using Hα Spectral Images Taken by SMART/SDDI

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 Hα 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 Hα spectral images taken by the Solar Magnetic Activity Research Telescope/Solar Dynamics Doppler Imager at Hida Observatory, Kyoto University. All the analyzed events show emission relative to the pre-event state and the changes in their Hα equivalent widths are all on the orders of 10−4 Å. Sun-as-a-star Hα spectra exhibit different features depending on the causes of the emission: (i) flares show emission at the Hα 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 Hα line center, accompanied by blueshifted/redshifted absorption; notably, the disappearance of dark filaments leads to the apparent enhancement of the Hα line center emission, and (iii) eruptions of off-limb prominences show blueshifted/redshifted 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 redshifted absorptions in Sun-as-a-star Hα spectra lead to coronal mass ejections (CMEs). This result suggests that even if the falling components of stellar filament eruptions are detected as redshifted absorptions in Hα spectra, such stellar filament eruptions may also develop into CMEs.