Search Publications
High-frequency predictions for number counts and spectral properties of extragalactic radio sources. New evidence of a break at mm wavelengths in spectra of bright blazar sources
de Zotti, G.; Martínez-González, E.; Toffolatti, L. +1 more
We present models to predict high-frequency counts of extragalactic radio sources using physically grounded recipes to describe the complex spectral behaviour of blazars that dominate the mm-wave counts at bright flux densities. We show that simple power-law spectra are ruled out by high-frequency (ν ≥ 100 GHz) data. These data also strongly const…
Wang-Sheeley-Arge-Enlil Cone Model Transitions to Operations
Odstrcil, Dusan; Pizzo, Vic; Millward, George +3 more
The National Weather Service's (NWS) Space Weather Prediction Center (SWPC) is transitioning the first large-scale, physics-based space weather prediction model into operations on the NWS National Centers for Environmental Prediction (NCEP) supercomputing system (see also C. Schultz, Space weather model moves into prime time, Space Weather, 9, S03…
Magnetic reconnection as an element of turbulence
Carbone, V.; Matthaeus, W. H.; Wan, M. +6 more
In this work, recent advances on the study of reconnection in turbulence are reviewed. Using direct numerical simulations of decaying incompressible two-dimensional magnetohydrodynamics (MHD), it was found that in fully developed turbulence complex processes of reconnection locally occur (Servidio et al., 2009, 2010a). In this complex scenario, re…
The End of Helium Reionization at z ~= 2.7 Inferred from Cosmic Variance in HST/COS He II Lyα Absorption Spectra
Richter, Philipp; Hennawi, Joseph F.; Worseck, Gábor +6 more
We report on the detection of strongly varying intergalactic He II absorption in HST/COS spectra of two z em ~= 3 quasars. From our homogeneous analysis of the He II absorption in these and three archival sightlines, we find a marked increase in the mean He II effective optical depth from < τ_{eff,He II}> ≃ 1 at z ~= 2.3 to < τ…
Hubble Space Telescope Observations of Main-belt Comet (596) Scheila
Mutchler, Max; Jewitt, David; Agarwal, Jessica +2 more
We present Hubble Space Telescope Observations of (596) Scheila during its recent dust outburst. The nucleus remained point-like with absolute magnitude HV = 8.85 ± 0.02 in our data, equal to the pre-outburst value, with no secondary fragments of diameter >=100 m (for assumed albedos 0.04). We find a coma having a peak scattering cro…
Interpreting the Properties of Solar Energetic Particle Events by Using Combined Imaging and Modeling of Interplanetary Shocks
St. Cyr, O. C.; Szabo, A.; Rouillard, A. P. +10 more
Images of the solar corona obtained by the Solar-Terrestrial Relations Observatory (STEREO) provide high-cadence, high-resolution observations of a compression wave forming ahead of a fast (940 km s-1) coronal mass ejection (CME) that erupted at ~9:00 UT on 2010 April 03. The passage of this wave at 1 AU is detected in situ by the Advan…
Spectral classification of O2-3.5 If*/WN5-7 stars
Walborn, Nolan R.; Crowther, Paul A.
An updated classification scheme for transition O2-3.5 If*/WN5-7 stars is presented, following recent revisions to the spectral classifications for O and WN stars. We propose that O2-3.5 If*, O2-3.5 If*/WN5-7 and WN5-7 stars may be discriminated using the morphology of Hβ to trace increasing wind density as follows: purely in absorption for O2-3.5…
Transport of solar wind fluctuations: A two-component model
Matthaeus, W. H.; Smith, C. W.; Oughton, S. +2 more
We present a new model for the transport of solar wind fluctuations which treats them as two interacting incompressible components: quasi-two-dimensional turbulence and a wave-like piece. Quantities solved for include the energy, cross helicity, and characteristic transverse length scale of each component, plus the proton temperature. The developm…
What Dominates the Coronal Emission Spectrum During the Cycle of Impulsive Heating and Cooling?
Klimchuk, J. A.; Bradshaw, S. J.
The "smoking gun" of small-scale, impulsive events heating the solar corona is expected to be the presence of hot (>5 MK) plasma. Evidence for this has been scarce, but has gradually begun to accumulate due to recent studies designed to constrain the high-temperature part of the emission measure distribution. However, the detected hot component…
Transiting exoplanets from the CoRoT space mission. XV. CoRoT-15b: a brown-dwarf transiting companion
Mazeh, T.; Aigrain, S.; Alonso, R. +46 more
We report the discovery by the CoRoT space mission of a transiting brown dwarf orbiting a F7V star with an orbital period of 3.06 days. CoRoT-15b has a radius of 1.12+0.30-0.15 {R}_Jup and a mass of 63.3 ± 4.1 {M}_Jup, and is thus the second transiting companion lying in the theoretical mass domain of brown dwarfs. CoRoT-15b …