Abstract
Records of radiation intensity as a function of time and frequency (dynamic spectra) have been profitably used as a probe of the Sun's corona for many years. Motivated by the possibility of using the frequency domain to constrain theoretical models of coherent microwave emission from red dwarf (dMe) flare stars, we have used the Very Large Array in spectral-line mode at 1.4 GHz to obtain the first dynamic spectra of stellar sources other than the Sun. Two very intense, highly circularly polarized, microwave outbursts were observed on the dMe flare star UV Get (L726-8B), in addition to a slowly varying, unpolarized component. One outburst was purely left circularly polarized and showed no variations as a function of frequency across the 41 MHz band, whereas the other was as much as 70% right-circularly polarized and showed distinct variations with frequency. Although the slowly varying emission is probably due to incoherent gyrosynchrotron emission, the two flaring events are the result of coherent mechanisms. We interpret the coherent emission in terms of plasma radiation and the cyclotron maser instability.
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Bastian, T., Bookbinder, J. First dynamic spectra of stellar microwave flares. Nature 326, 678–680 (1987). https://doi.org/10.1038/326678a0
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DOI: https://doi.org/10.1038/326678a0
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