A coronal mass ejection event cross-identified by both plasma motion and coronal dimming on AB Dor

As one of the most violent phenomena known from the Sun, coronal mass ejections (CMEs), associated with escaping plasma energized by magnetic reconnection events, may lead to mass and angular momentum loss and cause very severe space weather disturbances around the Earth. CMEs are also thought to play key roles in stellar evolution, star-planet interaction and planetary habitability. On the Sun, CMEs have been studied intensively using the direct-imaging technique. For active stars, CMEs are expected to occur more frequently and strongly because of their higher activity levels reflecting by various statistics, yet the detection of stellar CMEs is quite challenging. So far only a handful of candidates have been reported, but all of them were identified by single indicator in a rather ambiguous fashion (Moschou et al, 2019; Argiroffi et al, 2019; Leitzinger and Odert, 2022). Here we report the high confidence discovery and characterization of a superflare-associated CME event on the rapidly rotating active star AB Dor, cross-identified by several diagnostics from solar CMEs. Using time-resolved high-resolution X-ray spectroscopy of a superflare observed with the onboard Reflection Grating Spectrometer (RGS) of the X-ray Multi-Mirror Mission (XMM-Newton) telescope (Jansen et al, 2001), we have detected coronal dimming by a decrease of electron density (n _e ) at the flare onset and decreases of flux, temperature ( T ) and emission measure (EM) at the end of decay phase, along with plasma motion indicating a high speed escape at $v_b sim 725 \pm 200\,\mathrm{km\,s}^{−1}$ . These indicators robustly suggest the occurrence of a stellar CME event in analogy to the well known solar counterparts. We highlight the feasibility of searching for stellar CMEs in large X-ray spectroscopic archives of the XMM-Newton , Chandra , etc. by more detailed analyses.