Filament Eruptions as seen in the Sun-as-a-star H-alpha Spectrum
| Nugget | |
|---|---|
| Number: | 530 |
| 1st Author: | Junyi ZHANG |
| 2nd Author: | Yijun HOU |
| Published: | July 6, 2026 |
| Next Nugget: | TBD |
| Previous Nugget: | Particle Pressure and CMEs, Streamer Blow-out CMEs and Particle Pressure |
Introduction
Solar filament/prominence eruptions are among the most energetic phenomena in the solar atmosphere and are major drivers of space weather. Their geoeffectiveness depends partly on where they occur on the Sun. For stars beyond the Sun, however, we cannot obtain spatially resolved images - they are observed as unresolved points. When an eruption happens in a localized region of a stellar atmosphere, can we infer its approximate source location (near disk center or limb, front side or far side, active region or quiet Sun) from subtle changes in the star's integrated spectrum?
The answer is Yes. We show (Ref. [1]) that filaments/prominences at different locations display distinct radiative and dynamical signatures during eruption, leaving identifiable imprints in the integrated spectrum. Using high-resolution full-disk Hα spectroscopic data from the Chinese Hα Solar Explorer (CHASE) we have obtained clear spectral fingerprints for each source-location category. The tool we use is the dynamic spectrum, with spectrograms displaying the spectrally-resolved Hα line profile as a function of time.
Signatures
On-disk vs. Limb: the line wings
The primary observational difference between on-disk and limb eruptions arises from the contrasting Hα appearance of filaments against their backgrounds. On the disk, filaments appear as dark absorption structures; when they erupt, cool dense material moving toward the observer blocks background radiation, producing blue-wing absorption in the integrated spectrum (see the magenta ellipse in Figure 1. b1). At the limb, prominences appear as bright emission structures against the dark background; erupting material produces blue-wing or red-wing emission signals (see the yellow ellipse in Figure 1. b2). Thus, the presence of emission in the far Hα wings is a strong indicator that the eruption occurred at the limb; otherwise, it is more likely an on-disk event.
On-disk Active-region vs. Quiet Sun: Line-Center Intensity
For on-disk filament eruptions, the magnetic environment (strong active-region fields versus weak quiet-Sun fields) leaves a clear imprint in the line-center intensity. Active-region filament eruptions are often accompanied by strong flare ribbons, so the integrated Hα spectrum is dominated by enhanced line-center emission, line broadening, and red asymmetry, which are strong initially and gradually weaken (see Figure 2 b1). The erupting filament's blue-wing absorption may be overwhelmed by the ribbon emission and become invisible. In quiet-region filament eruptions, flare ribbon signals are much weaker; the most prominent feature is blue-wing absorption from the erupting filament (Ref. [2]), with weak line-center emission that varies little (arising from the disappearance of filament material, see Figure 2 b2). Thus, the intensity and evolution of line-center emission serve as a proxy for the magnetic field strength of the source region.
Limb Active-region vs. Quiet Sun: Single Wing vs. Both Wings
Limb eruptions from different magnetic environments also exhibit distinct signatures. Active-region prominences are compact, fast-evolving, and often produce collimated high-speed ejections, resulting in single-wing (blue or red) emission that drifts rapidly and lasts for a short duration (see the yellow ellipse in Figure 1, b2 and b3). Quiet-region prominences are large-scale, slowly rising, and undergo significant expansion. Their integrated spectra show emission signals drifting slowly from line center toward both wings simultaneously (see Figure 3 b1), lasting for a long time, and later developing line-center absorption (arising from the disappearance of large-scale prominence material, see the magenta ellipse in Figure 3 b1 and b2). The combination of dual-wing emission, long duration, and late-phase line-center absorption is the unique signature of large-scale quiet-region limb prominence eruptions.
From Solar Templates to Stellar Fingerprint Decoding
In the past, when blue-shifted absorption or emission was seen in stellar Hα spectra, it was often attributed broadly to either an on-disk filament or a limb prominence eruption, without further localization. The solar "spectral atlas" reported here now provides a systematic template for comparison. We have already re-examined some published stellar eruption observations and found that the blue-wing emission event reported in Ref. [3] matches the spectral characteristics of a solar far-side limb eruption, while the event reported in Ref. [4] is consistent with a front-side limb eruption. This demonstrates the immediate applicability of our solar templates to stellar data.
Conclusions
Our comparative analysis of seven solar filament/prominence eruptions with different source locations reveals that Sun-as-a-star Hα spectroscopy can diagnose both the eruption site and its magnetic environment. These results provide a direct observational framework for interpreting stellar Hα spectra. While our study is based on seven representative events, we note that real eruptions can be more complexeruptions from different locations can share similarities, and those from the same location can exhibit variations. As a result, we will also apply this diagnostic framework to a larger statistical sample of fliament eruptions and use data-reconstruction data-reconstruction simulations to systematically vary parameters such as filament location, area, density, and velocity, quantitatively linking initial plasma conditions to integrated spectral signatures in our future works. The ultimate goal is to build a "spectral bridge" connecting solar and stellar atmospheric eruptions, providing a reliable ruler for interpreting eruptive activity on exoplanet host stars and assessing the true impact of stellar magnetic activity on planetary habitability.