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A stellar flare−coronal mass ejection event revealed by X-ray plasma motions


Coronal mass ejections (CMEs), often associated with flares1,2,3, are the most powerful magnetic phenomena occurring on the Sun. Stars show magnetic activity levels up to ten thousand times higher4, and CME effects on stellar physics and circumstellar environments are predicted to be substantial5,6,7,8,9. 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 the High Energy Transmission Grating Spectrometer onboard the Chandra X-ray Observatory space telescope, we distinctly detected Doppler shifts in S xvi, Si xiv and Mg xii lines that indicate upward and downward motions of hot plasmas (around 10–25 MK) within the flaring loop, with velocities of 100–400 km s−1, in agreement with a model of a flaring magnetic tube. Most notably, we also detected a later blueshift in the O viii line that reveals an upward motion, with velocity 90 ± 30 km s−1, of cool plasma (about 4 MK), that we ascribe to a CME coupled to the flare. From this evidence we were able to derive a CME mass of \(1\!.\!2_{ - 0.8}^{ + 2.6} \times 10^{21}\) g and a CME kinetic energy of \(5\!.\!2_{ - 3.6}^{ + 27.7} \times 10^{34}\) erg. These values provide clues in the extrapolation of the solar case to higher activity levels in other stars, suggesting that CMEs could indeed be a major cause of mass and angular momentum loss.

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Fig. 1: Observed X-ray spectra and light curve of HR 9024.
Fig. 2: Time-resolved line fits.
Fig. 3: Comparison between observed and predicted velocities.
Fig. 4: Extrapolation of the solar flare−CME relation.

Data availability

The Chandra dataset analysed in this work (ObsID 1892) can be accessed from The data that support plots and findings of this study are available from the corresponding author upon reasonable request.


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We acknowledge a modest financial contribution from the ASI-INAF agreement n.2017-14.H.O.

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Authors and Affiliations



C.A., F.R., J.J.D., A.C., P.T., R.B., M.M., S.O. and G.P. contributed to scientific discussion and writing of the text. C.A. and J.J.D. contributed to analysis of observational data. F.R. contributed to the hydrodynamic model development, and C.A. to the synthesis of the model line profile.

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Correspondence to C. Argiroffi.

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Peer review information: Nature Astronomy thanks Krisztian Vida and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Figures 1–2, Supplementary Tables 1–2.

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Argiroffi, C., Reale, F., Drake, J.J. et al. A stellar flare−coronal mass ejection event revealed by X-ray plasma motions. Nat Astron 3, 742–748 (2019).

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