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Flares are intense explosions on the solar and stellar surfaces, and solarflares are sometimes accompanied by filament or prominence eruptions. Recently,a large filament eruption associated with a superflare on a solar-type star EKDra was discovered for the first time. The absorption of the H$\alpha$ spectruminitially exhibited a blueshift with the velocity of $510$ (km s$^{-1}$), anddecelerated in time probably due to gravity. Stellar coronal mass ejections(CMEs) were thought to occur, although the filament eruption did not exceed theescape velocity under the surface gravity. To investigate how such filamenteruption occur and whether CMEs are associated with the filament eruption ornot, we perform one-dimensional hydrodynamic simulation of the flow along anexpanding magnetic loop emulating a filament eruption under adiabatic andunsteady conditions. The loop configuration and expanding velocity normal tothe loop are specified in the configuration parameters, and we calculate theline-of-sight velocity of the filament eruption using the velocities along andnormal to the loop. We found that (i) the temporal variations of the H$\alpha$spectrum for EK Dra can be explained by falling filament eruption in the loopwith longer time and larger spatial scales than that of the Sun, and (ii) thestellar CMEs are also thought to be associated with the filament eruption fromthe superflare on EK Dra, because the rarefied loop unobserved in the H$\alpha$spectrum needs to expand faster than the escape velocity, whereas the observedfilament eruption does not exceed the escape velocity.

Simple Model for Temporal Variations of H$\alpha$ Spectrum by an Eruptive Filament from a Superflare on a Solar-type Star