Simultaneous Multiwavelength Observations of Magnetic Activity in Ultracool Dwarfs. II. Mixed Trends in VB 10 and LSR 1835+32 and the Possible Role of Rotation

As part of our ongoing investigation of magnetic activity in ultracool dwarfs we present simultaneous radio, X-ray, UV, and optical observations of LSR1835+32 (M8.5), and simultaneous X-ray and UV observations of VB10 (M8), both with a duration of about 9 hr. LSR1835+32 exhibits persistent radio emission, and H alpha variability on timescales of 0.5-2 hr. The detected UV flux is consistent with photospheric emission, and no X-ray emission is detected to a deep limit of [image]. The H alpha and radio emission are temporally uncorrelated, and the ratio of radio to X-ray luminosity exceeds the correlation seen in F-M6 stars by >[image]. The lack of radio variability during four rotations of LSR1835+32 requires a uniform stellar-scale field of similar to 10 G, and indicates that the H alpha variability is dominated by much smaller scales,