  Coronal mass ejections (CMEs), often associated with flares, are the most
powerful magnetic phenomena occurring on the Sun. Stars show magnetic activity
levels up to 10^4 times higher, and CME effects on stellar physics and
circumstellar environments are predicted to be significant. However, stellar
CMEs remain observationally unexplored. Using time-resolved high-resolution
X-ray spectroscopy of a stellar flare on the active star HR 9024 observed with
Chandra/HETGS, we distinctly detected Doppler shifts in S XVI, Si XIV, and Mg
XII lines that indicate upward and downward motions of hot plasmas (~10-25 MK)
within the flaring loop, with velocity v~100-400 km/s, in agreement with a
model of flaring magnetic tube. Most notably, we also detected a later
blueshift in the O VIII line which reveals an upward motion, with v=90+/-30
km/s, of cool plasma (~4 MK), that we ascribe to a CME coupled to the flare.
From this evidence we were able to derive a CME mass of 1x10^21 g and a CME
kinetic energy of 5x10^34 erg. These values provide clues in the extrapolation
of the solar case to higher activity levels, suggesting that CMEs could indeed
be a major cause of mass and angular momentum loss.
