Prominence formation and ejection in cool stars

TL;DR

This paper models prominence formation and ejection in cool stars, showing that prominences can significantly impact orbiting exoplanets, especially around M dwarfs, with implications for planetary atmospheres.

Contribution

It introduces a model for prominence support in cool stars using magnetic and gravitational energies, predicting prominence masses and ejection rates consistent with observations.

Findings

Prominence masses are typically 10^{16}-10^{17} g.

Ejection frequency is about 0.4 days.

Frequent prominence ejections can impact exoplanet atmospheres.

Abstract

The observational signatures of prominences have been detected in single and binary G and K type stars for many years now, but recently this has been extended to the M dwarf regime. Prominences carry away both mass and angular momentum when they are ejected and the impact of this mass on any orbiting planets may be important for the evolution of exoplanetary atmospheres. By means of the classification used in the massive star community, that involves knowledge of two parameters (the co-rotation and Alfv\'en radii, $r_K$ and $r_A$), we have determined which cool stars could support prominences. From a model of mechanical support, we have determined that the prominence mass $m_p/M_\star=(E_M/E_G)(r_\star/r_K)^2 F$ where $E_MB_\star^2r_\star^3$ and $E_G = GM_\star^2/r_\star$ are magnetic and gravitational energies and $F$ is a geometric factor. Our calculated masses and ejection frequencies (typically $10^{16}-10^{17}$g and 0.4 d, respectively) are consistent with observations and are sufficient to ensure that an exoplanet orbiting in the habitable zone of an M dwarf could suffer frequent impacts.