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Stellar radio emission can measure a star's magnetic field strength and structure, plasma density, and dynamics, and the stellar wind pressure impinging on exoplanet atmospheres. However, properly interpreting the radio data often requires temporal baselines that cover the rotation of the stars, orbits of their planets, and any longer-term stellar activity cycles. Here we present our monitoring campaign on the young, active M dwarf AU Microscopii with the Australia Telescope Compact Array between 1.1 and 3.1 GHz. With over 250 h of observations, these data represent the longest radio monitoring campaign on a single main-sequence star to date. We find that AU Mic produces a wide variety of radio emission, for which we introduce a phenomenological classification scheme predicated on the polarisation fraction and time-frequency structure of the emission. Such a classification scheme is applicable to radio emission from other radio-bright stars. The six types of radio emission detected on AU Mic can be broadly categorised into five distinct types of bursts, and broadband quiescent emission. We find that the radio bursts are highly circularly polarised and periodic with the rotation period of the star, implying that the emission is beamed. It is therefore most likely produced by the electron cyclotron maser instability. We present a model to show that the observed pattern of emission can be explained by emission from auroral rings on the magnetic poles. The total intensity of the broadband emission is stochastic, but we show that its circular polarisation fraction is also periodic with the rotation of the star. Such a periodicity in the polarised fraction of emission has not been observed on an M dwarf before. We present a qualitative model to describe the periodicity in the polarisation fraction of the broadband emission, using low-harmonic gyromagnetic emission. Using a simple qualitative model, we infer a magnetic obliquity of at least 20° from the observed variation in polarisation fraction. Finally, we show that the radio emission might be evolving on long timescales, hinting at a potential stellar magnetic activity cycle. [ABSTRACT FROM AUTHOR]

Apep is the brightest and most luminous non-thermal colliding-wind binary by over an order of magnitude. It has been suggested from infrared observations that one of the Wolf–Rayet stars in Apep is launching an anisotropic wind. Here we present radio observations of Apep from 0.2 to 20 GHz taken over 33 yr. The spectrum reveals an extremely steep turnover in the flux density at low frequencies, where the flux density decreases by two orders of magnitude over only 325 MHz of bandwidth. This exponential decline is best described by free–free absorption, with a turnover frequency at 0.54 ± 0.01 GHz. Above the turnover, the spectrum is well described by a power-law and a high-frequency cut-off likely caused by inverse-Compton cooling. The light curve of Apep shows significant variation over the observing period, with Apep brightening by over 50 mJy in a span of 25 yr at 1.4 GHz. Models that assume spherical winds do not replicate all of the structure evident in the radio light curve. We derived a model that allows one of the winds in the system to be anisotropic. This anisotropic model recovers most of the structure of the light curve and is a significantly better statistical fit to the data than the spherical wind model. We suggest such a result is independent support that one of the Wolf–Rayet stars in Apep is launching an anisotropic wind. If the anisotropic wind model is correct, we predict a ∼25 per cent decrease of the 1.4 GHz flux density of Apep over the next 5 yr. [ABSTRACT FROM AUTHOR]