June
2026
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2026MNRAS.549ag837D
Authors
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Daley-Yates, Simon
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Jardine, Moira M.
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Bouma, Luke
Abstract
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We investigate the survival of dust trapped in magnetically confined cool gas clouds (or prominences) around rapidly rotating M dwarfs exhibiting the 'scallop-shell' light-curve morphology. Using a two-dimensional magnetohydrodynamic simulation, we extend previous coronal prominence models to include a passive tracer field to allow for a single injection of collisionally charged dust grains. The tracer evolution reveals how recurrent centrifugal breakouts ─ the slingshot process ─ remove dust and gas from the prominence while chromospheric evaporation replenishes gas from below. For our simulated star, which has $R_{\ast } = 0.6 \mathrm{ R}_{\odot }$, $M_{\ast } = 0.3 {\rm M}_{\odot }$, and $P_{\ast } = 0.32$ d, the resulting dust content decays exponentially with a minimum half-life of approximately six stellar rotations, representing a lower limit set by our assumption of fully coupled dust and gas dynamics. Synthetic velocity-phase diagnostics show a single, phase-locked feature that fades steadily, reproducing the behaviour of dips seen in TESS and K2 light curves. Comparison with observed river plots suggests a natural classification: (i) persistent, non-decaying features formed by quiescent prominences below co-rotation; (ii) gradually fading features produced by slingshot prominences near co-rotation; and (iii) abrupt disappearances linked to magnetic reconnection and flare-driven ejections. These results demonstrate that dust-bearing prominences ─ undergoing repeated slingshots ─ can persist for tens of rotations, linking the observed longevity of the scallop-shell photometric features with the dynamic cycle of prominence slingshot ejections.
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