| Unlocking the Origins of Ultracool Dwarf Radio Emission |
| Anna Hughes |
| University of British Columbia, Vancouver, Canada |
| M dwarfs are the most common stars in the Milky Way, comprising 75% of all stars. While early-type M dwarfs are notorious for their flaring and variability, the magnetic activity and associated radio emission mechanisms of objects later than spectral type M7 are poorly understood. Based on empirical trends in the X-ray and radio luminosities of more massive stars, these ultracool dwarfs, brown dwarfs and stars with spectral type later than M7, were not expected to produce significant radio emission. Defying expectations, strong non-thermal emission has been observed from some UCDs in the 1–10 GHz range, where emission is expected to peak. Radio emission from ultracool dwarfs is typically attributed to global aurorae, but in this frequency range gyrosynchrotron radiation could also plausibly produce detectable emission. Since these two emission mechanisms originate in very different physical processes, a key part of characterizing the magnetic activity of ultracool dwarfs is determining which – or both – radio emission mechanisms are present. Observations at higher radio frequencies, where gyrosynchrotron is expected to dominate and auroral emission is expected to be non-detectable, can break the degeneracy. Beyond informing magnetic models of ultracool dwarfs, the presence of gyrosynchrotron radiation may have consequences for planets in orbit around these objects, as reconnection events can threaten the stability of planetary atmospheres. We present high radio frequency observations of 5 ultracool dwarfs, 2 of which were non-detections, 3 that were detected with bright emission indicative of gyrosynchrotron radiation. |