Coronal mass ejections and type II radio emission variability during a magnetic cycle on the solar-type star $\epsilon$ Eridani

TL;DR

This study models stellar coronal mass ejections and their associated type II radio bursts on $\, ext{epsilon}$ Eridani, highlighting how magnetic geometry influences detectability and estimating their radio emission duration within LOFAR's observational range.

Contribution

It provides the first detailed simulations of CME radio emission variability on $\, ext{epsilon}$ Eridani$ and assesses how magnetic field configurations affect observability of these stellar eruptions.

Findings

Type II bursts last 20-30 minutes within LOFAR frequency range.

Polar CMEs are more detectable than equatorial ones due to magnetic geometry.

CME mass-loss contribution can reach up to 50% of stellar wind mass-loss rate.

Abstract

We simulate possible stellar coronal mass ejection (CME) scenarios over the magnetic cycle of $\epsilon$ Eridani (18 Eridani; HD 22049). We use three separate epochs from 2008, 2011, and 2013, and estimate the radio emission frequencies associated with these events. These stellar eruptions have proven to be elusive, although a promising approach to detect and characterise these phenomena are low-frequency radio observations of potential type II bursts as CME induced shocks propagate through the stellar corona. Stellar type II radio bursts are expected to emit below 450 MHz, similarly to their solar counterparts. We show that the length of time these events remain above the ionospheric cutoff is not necessarily dependent on the stellar magnetic cycle, but more on the eruption location relative to the stellar magnetic field. We find that these type II bursts would remain within the frequency range of LOFAR for a maximum of 20-30 minutes post-eruption for the polar CMEs, (50 minutes for 2nd harmonics). We find evidence of slower equatorial CMEs, which result in slightly longer observable windows for the 2008 and 2013 simulations. Stellar magnetic geometry and strength has a significant effect on the detectability of these events. We place the CMEs in the context of the stellar mass-loss rate (27-48 $\times$ solar mass-loss rate), showing that they can amount to 3-50% of the stellar wind mass-loss rate for $\epsilon$ Eridani. Continuous monitoring of likely stellar CME candidates with low-frequency radio telescopes will be required to detect these transient events.