2001A&A...370.1000B

Recent images in the radio of UV Ceti show two intense emission regions above the magnetic poles of the star. The emission is overwhelmingly right hand circularly polarized with 100% right hand polarization at 3 cm and 6 cm wavelengths during flares. This high degree of polarization rules out gyrosynchrotron emission. In this article we propose that such emission can be produced by a coherent cyclotron maser driven by field aligned electrons moving into an increasing magnetic field. Conservation of the first adiabatic invariant causes the electron beam to increase its pitch angle. This produces a broad region on the distribution function and the possibility of producing a positive slope in the perpendicular velocity space. Such distribution functions are common in magnetic mirror type geometries and are possible sources of free energy leading to electromagnetic emission by a cyclotron maser instability mechanism.