Auroral Radio Emission from Stars: the case of CU Virginis

TL;DR

This study observes CU Virginis's unique auroral radio emissions, revealing their beamed nature, propagation effects, and implications for understanding stellar and planetary magnetospheres, including precise stellar spin-down measurements.

Contribution

First detailed analysis of CU Virginis's auroral radio emission, linking stellar magnetospheres to planetary auroral processes and enabling accurate stellar rotation measurements.

Findings

Confirmed two highly polarized pulses per rotation with flux up to 20 mJy.

Detected frequency-dependent time delays indicating propagation effects.

Suggested similarities between stellar and planetary auroral radio emissions.

Abstract

CU Virginis is a rapidly rotating Magnetic Chemically Peculiar star with at present unique characteristics as radio emitter. The most intriguing one is the presence of intense, 100% circularly polarized radiation ascribed to Cyclotron Maser. Each time the star rotates, this highly beamed emission points two times toward the Earth, like a pulsar. We observed CU Vir in April 2010 with the EVLA in two bands centered at 1450 and 1850 MHz. We covered nearly the whole rotational period, confirming the presence of the two pulses at a flux density up to 20 mJy. Dynamical spectra, obtained with unprecedented spectral and temporal sensitivity, allow us to clearly see the different time delays as a function of the frequency. We interpret this behaviour as a propagation effect of the radiation inside the stellar magnetosphere. The emerging scenario suggests interesting similarities with the auroral radio emission from planets, in particular with the Auroral Kilometric Radiation (AKR) from Earth, which originates at few terrestrial radii above the magnetic poles and was only recently discovered to be highly beamed. We conclude that the magnetospheres of CU Vir, Earth and other planets, maybe also exoplanets, could have similar geometrical and physical characteristics in the regions where the cyclotron maser is generated. In addition, the pulses are perfect "markers" of the rotation period. This has given us for the first time the possibility to measure with extraordinary accuracy the spin down of a star on or near the main sequence.