2025ApJ...991...54C

Stellar flares are frequently accompanied by prominence eruptions, coronal mass ejections (CMEs), and other forms of plasma motion. Based on the long-term high-resolution spectroscopic monitoring data set of the RS CVn-type star II Pegasi (II Peg), we search for stellar prominence eruptions and potential CMEs by investigating asymmetric signatures in the H_α and H_β line profiles during the flare events. We observed seven optical flares with asymmetric spectral profiles, releasing low limit energies of 10³³-10³⁴ erg in the H_α line. Five of these flares were associated with six potential CMEs, identified through the Doppler-shifted emission signatures in the chromospheric line profiles, particularly the H_α line. The mass estimates for the CME candidates range from 10¹⁹ to 10²⁰ g, while the kinetic energies are calculated to be around 10³³-10³⁴ erg. The most massive CME candidate was simultaneously recorded in the H_α, H_β, and He I D₃ lines. For II Peg, the possible flare-CME association rate is about 30%. There were also some redshifted excess absorption signatures in the H_α line profiles. These signatures could not only be observed in the flaring spectra but also in the spectra without flare, which could be interpreted as features resulting from flare-driven coronal rain and quiescent rain, respectively.