Barnali Das (CSIRO)

Barnali Das colloquium: Coherent radio emission from hot magnetic stars

Kensington

Abstract

Hot magnetic stars are the perfect laboratories for understanding stellar magnetospheric phenomena due to the fact that their fields are extremely stable throughout their lifetimes, and also have very simple topologies (dipolar in most cases). Their strong stellar winds interact with the magnetic fields giving rise to co-rotating magnetospheres extending up to several tens of stellar radii. The magnetosphere manifests itself via emission over a wide range of the electromagnetic spectrum, starting from radio to X-ray. These emissions convey different kinds of information, and together, they act as probes for wind-magnetic field interplay. Among the different emissions that these magnetospheres produce, the latest discovered, and consequently, the least understood one is the coherent radio emission, also referred to as auroral radio emission. This is produced by electron cyclotron maser emission (ECME, the same mechanism that drives auroral radio emission from magnetic ultracool dwarfs and planets). In my talk, I will take you on our journey towards demystifying this phenomenon, starting with some serendipitous discoveries, followed by a systematic sub-GHz survey, which ironically led to the discoveries of many more unexplained characteristics, including discovery of radio flares, in addition to providing solutions to existing problems. I will present the results that we have obtained so far regarding ECME incidence, wideband properties and stability, and potential scenarios to explain the observations. I will end with my future plan to obtain more definitive insights about magnetospheric operation and the role that ATNF instruments can play in achieving that goal.