Mapping radio emitting-region on low-mass stars and brown dwarfs

S Yu,A.L Mackinnon,J.G Doyle,G Hallinan

doi:10.1051/epjconf/20111606013

Abstract

Strong magnetic activity in ultracool dwarfs (UCDs, spectral classes later than M7) have emerged from a number of radio observations, including the periodic beams. The highly (up to 100%) circularly polarized nature of the emission point to an effective amplification mechanism of the high-frequency electromagnetic waves – the electron cyclotron maser (ECM) instability. Several anisotropic velocity distibution models of electrons, including the horseshoe distribution, ring shell distribution and the loss-cone distribution, are able to generate the ECM instability. A magnetic-field-aligned electric potential would play an significant role in the ECM process. We are developing a theoretical model in order to simulate ECM and apply this model to map the radio-emitting region on low-mass stars and brown dwarfs.

Highlights

The highly circularly polarized nature of the emission point to an effective amplification mechanism of the high-frequency electromagnetic waves – the electron cyclotron maser (ECM) instability
We are developing a theoretical model in order to simulate ECM and apply this model to map the radio-emitting region on low-mass stars and brown dwarfs
A large number of recent observations indicate that intense magnetic activity exists in ultracool dwarfs which have spectral type later than M7, including some brown dwarfs with L, T type spectra

Summary

INTRODUCTION

A large number of recent observations indicate that intense magnetic activity exists in ultracool dwarfs which have spectral type later than M7, including some brown dwarfs with L, T type spectra. Common features of the radio observation in these ultracool dwarfs are high brightness temperature and highly circular polarization emission, which suggest that the dominant radio emission mechanism in the ultracool dwarfs is the electron cyclotron maser (ECM) instability – direct wave magnification process of the free-space radiation modes [14]. This process could be induced by some kind of anisotropic velocity distributions of electrons, such as a loss-cone distribution, a ring shell distribution, or a horseshoe distribution. We describe the method and preliminary results

SIMULATION MODEL

PRELIMINARY RESULTS

DISCUSSION