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.

A Superflare on YZ Canis Minoris Observed by the Seimei Telescope and TESS: Red Asymmetry of Hα Emission Associated with White-light Emission

“…There could be a possibility that the strong overlying magnetic fields of the M dwarf may have suppressed a prominence eruption and CME, resulting in a significant reduction of the velocity (Alvarado-Gomez et al 2018). Moreover, it is possible that the strong chromospheric condensation during the impulsive phase of this superflare could have masked the faint blueshifted components that are associated with weak CMEs (Koller et al 2021;Otsu et al 2022). We expect that a larger sample of time-resolved spectroscopic observations, like those in this study, and simultaneous observations of the X-ray and UV bands will reveal more details about the relationships between redshifts (and blueshifts) and CMEs on stars in the future.…”

Unified Relationship between Cold Plasma Ejections and Flare Energies Ranging from Solar Microflares to Giant Stellar Flares

“…Consequently, the line-of-sight velocity and the kinetic energy are more likely to be underestimated in the stellar cases than in the solar cases. To understand the significance of this effect, we need further Sun-as-a-star analyses for the spectra of the cold plasma ejection (Namekata et al 2022;Otsu et al 2022).…”

Reconstructing the XUV Spectra of Active Sun-like Stars Using Solar Scaling Relations with Magnetic Flux

“…Here we use the Sun-as-a-star multimission data (spatially integrated data over the whole solar disk) over more than 10 yr to derive the power-law relations for XUV/FUV spectral bands. The Sun-as-a-star approach is a very powerful tool in understanding phenomena on stars that cannot be spatially resolved and has been widely used (e.g., Kretzschmar 2011;Maldonado et al 2019;Toriumi et al 2020;Namekata et al 2022aNamekata et al , 2022cOtsu et al 2022;. Section 2 describes the Sun-as-a-star data set used in our analysis.…”