325 MHz VLA Observations of Ultracool Dwarfs TVLM 513-46546 and 2MASS J0036+1821104

摘要: We present 325 MHz (90 cm wavelength) radio observations of ultracool dwarfs TVLM 513-46546 and 2MASS J0036+1821104 using the Very Large Array (VLA) in June 2007. Ultracool are expected to be undetectable at frequencies, yet 8.5 GHz (3.5 cm) 4.9 (6 have revealed sources with > 100 {\mu}Jy quiescent flux 1 mJy pulses coincident stellar rotation. The anomalous emission is likely a combination gyrosynchrotron cyclotron maser processes long-duration, large-scale magnetic field. Since characteristic frequency for each process scales directly field magnitude, lower frequencies may detectable from regions weaker strength. detect no significant or over multiple rotations, establishing 2.5{\sigma} total limits 795 942 respectively. Analysis an archival VLA 1.4 observation January 2005 also yields non-detection level < 130 . combined history (0.3 GHz) these suggests continuum spectrum which either flat inverted below 2-3 GHz. Further, if instability responsible pulsed observed on some dwarfs, our low-frequency non-detections suggest that active region high-frequency bursts confined within 2 radii driven by electron beams energies less than 5 keV.