A fast-filament eruption observed in the H$α$ spectral line. I. Imaging spectroscopy diagnostic

Abstract

Context. Solar filament eruptions usually appear to occur in association with the sudden explosive release of magnetic energy accumulated in long-lived arched magnetic structures. It is the released energy that occasionally drives fast-filament eruptions that can be source regions of coronal mass ejections. Aim. The goal of this paper is to investigate the dynamic processes of a fast-filament eruption by using unprecedented high-resolution full-disk H$α$ imaging spectroscopy observations. Methods. The whole process of the eruption was captured in a wide spectral window of the H$α$ line ($\pm9.0$ A). Applying the "cloud model" and obtaining two dimensional optical thickness spectra we derive the Doppler velocity, the true eruption profiles (height, velocity, and acceleration), and the trajectory of the filament eruption in 3D space. Results. The Doppler velocity maps show that the filament was predominantly blue-shifted. During the main and final process of the eruption, strongly blue-shifted materials are manifested traveling with velocities exceeding $250~km/s$. The spectral analysis further revealed that the erupting filament is made of multiple components, some of which were Doppler-shifted approximately to $-300 ~km/s$. It is found that the filament eruption attains a maximum true velocity and acceleration of about $600~km/s$ and $2.5~km/s^2$, respectively, and its propagation direction deviates from the radial direction. On the other hand, downflows manifested as red-shifted plasma close to the footpoints of the erupting filament move with velocities $45-125~ km/s$. We interpret these red-shifted signatures as draining material, and therefore mass loss of the filament that has implications for the dynamic and the acceleration process of the eruption. Furthermore, we have estimated the total mass of the H$α$ filament resulting in $\sim$$5.4\times10^{15}g$.