Coronal mass ejection precursors in Sun-like stars: Flux rope modelling and coronal signatures

Coronal mass ejections (CMEs) are among the most energetic manifestations of solar and stellar activity. In the Sun, they play a central role in space weather, while in more active stars, the solar paradigm indicates that they should be even more frequent and energetic. However, many CMEs predicted from stellar activity indicators remain undetected, suggesting that additional factors regulate their eruption and visibility. Understanding under which conditions CMEs successfully escape, are confined, or fail to erupt is therefore essential for interpreting stellar activity and its impact on surrounding environments. We aim to investigate how the escape or suppression of CMEs depends on both the local magnetic flux rope (MFR) properties and the large-scale magnetic field, even for weak values as observed in Sun-like stars. We performed magnetohydrodynamic (MHD) simulations based on a catastrophe MFR model, exploring variations in the flux rope mass, internal magnetic flux, position relative to the overlying large-scale magnetic field, and the strength of the strapping field. We also synthesised extreme ultraviolet (EUV) emission and estimated Doppler shifts to assess observable signatures. We identify three possible outcomes: (i) successful eruptions, (ii) confined eruptions in which the MFR is eroded by reconnection, and (iii) confined eruptions in which the MFR collapses onto the chromosphere. The likelihood of ejection depends on the relation between the flux rope’s magnetic flux and the strapping flux of the overlying magnetic cage. Photometry in the EUV clearly distinguishes only cases of collapse, while successful and eroded cases appear similar. However, a meaningful Doppler velocity measurement could help to distinguish between the first two scenarios, for instance, if the CME motion aligns with the line of sight or occurs at a favourable angle. Stronger background fields, heavier MFRs, and more symmetric magnetic structures enhance confinement and suppress ejections. Our results suggest that in Sun-like stars, stronger global fields may unexpectedly reduce CME occurrence by increasing magnetic confinement, thus altering their observable signatures.