Doppler-shifted Signatures in the Chromospheric Line Profiles of II Pegasi

Abstract

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$_{\alpha}$ and H$_{\beta}$ line profiles during the flare events. We observed seven optical flares with asymmetric spectral profiles, releasing low limit energies of $10^{33}$--$10^{34}$ erg in the H$_{\alpha}$ 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$_{\alpha}$ line. The mass estimates for the CME candidates range from $10^{19}$ to $10^{20}$ g, while the kinetic energies are calculated to be around $10^{33}$--$10^{34}$ erg. The most massive CME candidate was simultaneously recorded in the H$_{\alpha}$, H$_{\beta}$, and He I D$_{3}$ lines. For II Peg, the possible flare-CME association rate is about 30\%. There were also some redshifted excess absorption signatures in the H$_{\alpha}$ 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.