Superflares on Giant Stars

TL;DR

This paper investigates superflares on giant stars, including the Sun, proposing that anti-solar differential rotation could generate magnetic energy sufficient for superflares, supported by simple dynamo models.

Contribution

It introduces a mechanism linking anti-solar differential rotation to superflares, supported by simple dynamo models and observations of HK Lac.

Findings

Superflares observed on giant stars and the Sun could be explained by magnetic energy from anti-solar differential rotation.

Magnetic configurations with quadrupole symmetry have significantly higher energy, potentially causing superflares.

Simple models suggest anti-solar differential rotation can produce enough magnetic energy for superflares.

Abstract

The Kepler mission identified huge flares on various stars including some of solar type. These events are substantially more energetic than solar flares, and so they are referred to as superflares. Even a small probability of such a superflare on the Sun would be a menace to modern society. A flare comparable in energy with that of superflares was observed on 24th and 25th September on the binary HK Lac. Unlike the Kepler stars, there are observations of differential rotation for HK Lac. This differential rotation appears to be anti-solar. For anti-solar differential rotation, dynamo models can give magnetic activity waves of dipole symmetry as well as quasi-stationary magnetic configurations with quadrupole symmetry. The magnetic energy of such stationary configurations is usually about two orders of magnitude higher than that associated with activity waves. We believe that this mechanism could provide sufficient energy to produce superflares on late type stars, and present some simple models in support of this idea.