A number of radio-loud ultra cool dwarf stars (UCD) exhibit both continuous broadband and highly polarized pulsed radio emission. In order to determine the nature of the emission and the physical characteristics in the source region, we have made mul
ti-epoch, wideband spectral observations of TVLM 0513-46 and 2M 0746+20. We combine these observations with archival radio data to fully characterize both the temporal and spectral properties of the radio emission. The continuum spectral energy distribution can be well modeled using gyrosynchrotron emission from mildly relativistic electrons in a dipolar field. The pulsed emission exhibits a variety of time-variable characteristics, including frequency drifts, frequency cutoffs, and multiple pulses per period. For 2M 0746+20 we determine a pulse period consistent with previously determined values. We modeled locations of pulsed emission using an oblique rotating magnetospheric model with beamed electron cyclotron maser (ECM) sources. The best-fit models have narrow ECM beaming angles aligned with the local source magnetic field direction, except for one isolated burst from 2M 0746+20. For TVLM 0513-46, the best-fit rotation axis inclination is nearly orthogonal to the line of sight. For 2M 0746+20 we found a good fit using a fixed inclination i=36 deg, determined from optical observations. For both stars the ECM sources are located near feet of magnetic loops with radial extents 1.2Rs-2.7 Rs and surface fields 2.2 - 2.5 kG. These results support recent suggestions that radio over-luminous UCDs have a global `weak field non-axisymmetric magnetic topologies.
The active young protostar DG Tau has an extended jet that has been well studied at radio, optical, and X-ray wavelengths. We report sensitive new VLA full-polarization observations of the core and jet between 5 GHz and 8 GHz. Our high angular resolu
tion observation at 8 GHz clearly shows an unpolarized inner jet with a size 42 AU (0.35) extending along a position angle similar to the optical-X ray outer jet. Using our nearly coeval 2012 VLA observations, we find a spectral-index=+0.46+/-0.05, which combined with the lack of polarization, is consistent with bremsstrahlung (free-free) emission, with no evidence for a non-thermal coronal component. By identifying the end of the radio jet as the optical depth unity surface, and calculating the resulting emission measure, we find our radio results are in agreement with previous optical line studies of electron density and consequent mass-loss rate. We also detect a weak radio knot at 5 GHz located 7 from the base of the jet, coincident with the inner radio knot detected by Rodriguez et al. (2012) in 2009 but at lower surface brightness. We interpret this as due to expansion of post-shock ionized gas in the three years between observations.
The production of the lightest Higgs boson, $h^0$, in association with the lightest stop, $tilde{t}_{1}$, in the Minimal Supersymmetric Standard Model, is an interesting channel, as its cross section can be higher than Higgs production in association
with top quarks. Furthermore, the $tilde{t}_{1}tilde{t}^{*}_{1}h^{0}$ production rate is highly dependent on various Supersymmetric parameters. The mass, mixings, couplings and production cross sections relevant to the $tilde{t}_{1}tilde{t}^{*}_{1}h^{0}$ channel have been studied in the past. Here, we complement these analyses by performing a thorough decay study. We conclude that there is some scope for extracting this channel at the Large Hadron Collider, for suitable combinations of the Supersymmetric parameters, in several different decay channels of both the stop quarks and Higgs boson, the most numerically promising being the signature involving charm decays of the stops and bottom decay of the Higgs. This, in fact, remains true in the Supergravity inspired Minimal Supersymmetric Standard Model.
