# On the global and local magnetic fields in flare stars. Study of YZ CMi and OT Ser

## TL;DR

This paper investigates the rapid evolution of global magnetic fields in flare stars OT Ser and YZ CMi, proposing a mechanism where differential rotation generates local fields that dissipate energy through flares, with minimal impact on global fields.

## Contribution

It introduces a new model linking differential rotation to local magnetic field generation and magnetic braking in flare stars, supported by energy estimates and flare observations.

## Key findings

- Local magnetic fields dissipate energy during superflares.
- Global magnetic fields remain unaffected by local field dissipation.
- Differential rotation plays a key role in magnetic field evolution.

## Abstract

Global magnetic fields of flare stars can evolve rapidly, in time scale of hundreds or dozens of days. We believe, that such changes result from rapid superposition of local magnetic fields generated by differential rotation of those stars. We discuss possible mechanisms of generation and dissipation of local and global magnetic fields in sample flare stars OT Ser and YZ CMi. We propose mechanism of magnetic braking of these stars, in which differential rotation generates local magnetic fields, and eventually energy accumulated in local fields is radiated away by flares. We obtained estimates of the rotational energy and the energy of the global magnetic field of OT Ser and YZ CMi. We also show that the energy of the local magnetic fields dissipated during superflare of YZ CMi on 9 February 2008 (UT 20:22:00) did not influence the global magnetic field of this star.