Simple model for filament and prominence eruptions from superflares on a young solar-type star

Recently, large filament and prominence eruptions associated with superflares on a young solar-type star EK Draconis (EK Dra) were discovered for the first time (Namekata et al. 2022 & 2024). The absorption and emission of the Hα spectrum associated with the eruptions initially exhibited a blueshift, and decelerated in time probably due to gravity. Stellar coronal mass ejections (CMEs) are thought to have occurred, although the filament eruption did not exceed the escape velocity. To investigate how such a filament eruption occurred and whether CMEs were associated with the filament eruption or not, we perform a one-dimensional hydrodynamic simulation of the flow along an expanding magnetic loop emulating a filament eruption under adiabatic and unsteady conditions. We find that (i) the temporal variations of the Hα absorption for EK Dra can be explained by a falling filament eruption in the loop with longer time and larger spatial scales than that of the Sun, and (ii) the stellar CMEs are also thought to have been associated with the filament eruption from the superflare on EK Dra, because the rarefied loop unobserved in the Hα spectrum needs to expand faster than the escape velocity (Ikuta & Shibata 2024).  We also apply the simple model to the prominence eruption on EK Dra, and it is suggested that (iii) the temporal variation of Hα emission can be also explained simply by changing the line of sight as in the case of the filament eruption.