An application of a solar-type dynamo model for Epsilon Eridani

TL;DR

This paper develops a non-linear dynamo model for Epsilon Eridani, successfully reproducing observed short and long activity cycles and activity minima, demonstrating the model's ability to simulate stellar magnetic behavior.

Contribution

The study presents the first application of a first-principles non-linear dynamo model to Epsilon Eridani, capturing multiple activity cycles and minima.

Findings

The model reproduces observed 3-year and 13-year activity cycles.

The model explains short cycles via differential rotation and long cycles via meridional flows.

Simulated activity minima resemble the star's historical activity minimum.

Abstract

During the last decade, the relation between activity cycle periods with stellar parameters has received special attention. The construction of reliable registries of activity reveals that solar type stars exhibit activity cycles with periods from few years to decades and, in same cases, long and short activity cycles coexist suggesting that two dynamos could operate in these stars. In particular, Epsilon Eridani is an active young K2V star (0.8 Gyr), which exhibits a short and long-term chromospheric cycles of near 3 and 13-yr periods. Additionally, between 1985 and 1992, the star went through a broad activity minimum, similar to the solar Maunder Minimum-state. Motivated by these results, we found in Epsilon Eridani a great opportunity to test the dynamo theory. Based on the model developed in Sraibman & Minotti (2019), in this work we built a non linear axisymmetric dynamo for Epsilon Eridani. The time series of the simulated magnetic field components near the surface integrated in all the stellar disc exhibits both the long and short-activity cycles with periods similar to the ones detected from observations and also time intervals of low activity which could be associated to the broad Minimun. The short activity cycle associated to the magnetic reversal could be explained by the differential rotation, while the long cycle is associated to the meridional mass flows induced by the Lorentz force. In this way, we show that a single non-linear dynamo model derived from first principles with accurate stellar parameters could reproduce coexisting activity cycles.