27 research outputs found
The Pre-Main-Sequence Eclipsing Binary ASAS J052821+0338.5
In this paper we present the first results of a detailed spectroscopic and
photometric analysis of the V = 11.7m eclipsing binary ASAS J052821+0338.5.
With the FIES spectrograph at the Nordic Optical Telescope we have obtained a
series of high-resolution spectra (R=47000) covering the entire orbit of the
system. In addition we obtained simultaneous broadband photometry from three
small aperture telescopes. From these spectroscopic and photometric data we
have derived the system's orbital parameters and determined the fundamental
stellar parameters of the two components. Our results indicate that ASAS
J052821+0338.5 is a K1/K3 pre-main-sequence eclipsing binary, with component
masses of 1.38 M_sun and 1.33 M_sun and a period of 3.87 days, located at a
distance of 280 +/- 30 pc. The kinematics, physical location and the
evolutionary status of the two stars suggest that ASAS J052821+0338.5 is a
member of the approximately 11 Myr old Orion OB1a subassociation. The systems
also exhibits smooth 0.15m out-of-eclipse variations that are similar to those
found in RS CVn binaries. Furthermore the parameters we derived are consistent
with the 10-13 Myr isochrones of the popular Baraffe stellar evolutionary
models.Comment: 9 pages, 8 figures, to appear in A&
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Configuration control, fluctuations, and transport in low-collisionality plasmas in the ATF Torsatron
In low-collisionality plasmas confined in tokamaks and stellarators, instabilities driven by particles trapped in inhomogeneities of the magnetic fields could be important in increasing plasma transport coefficients. In the Advanced Toroidal Facility (ATF), an {ell} = 2, M = 12 field-period stellarator device with major radius R = 2.1 m, average plasma minor radius a = 0.27 m, central and edge rotational transforms {chi}{sub 0} {approx} 0.3, {chi}{sub a} {approx} 1, the effects of electron trapping in the helical stellarator field are expected to be important in plasmas with {bar n}{sub e} {approx} 5 {times} 10{sup 12} cm{sup {minus}3}, T{sub e0} {approx} 1 keV. Such plasmas have already been sustained for long-pulses (20 s) using 150--400 kW of 53.2-GHz ECH power at B = 0.95 T. Transport analysis shows that for {rho} = r/a {le} 1/3, the electron anomalous transport is {le}10 times the neoclassical value, while at {rho} = 2/3 it is 10--100 times neoclassical; this is compatible with expectations for transport enhancement due to dissipative trapped-electron modes. 4 refs., 3 figs
Results of WEBT, VLBA and RXTE monitoring of 3C 279 during 2006-2007
We present radio-to-optical data taken by the WEBT, supplemented by VLBA and
RXTE observations, of 3C 279. Our goal is to use this extensive database to
draw inferences regarding the physics of the relativistic jet. We assemble
multifrequency light curves with data from 30 ground-based observatories and
the space-based instruments, along with linear polarization vs. time in the
optical R band. In addition, we present a sequence of 22 images (with
polarization vectors) at 43 GHz at resolution 0.15 milliarcsec, obtained with
the VLBA. We analyse the light curves and polarization, as well as the spectral
energy distributions at different epochs, corresponding to different brightness
states. The IR-optical-UV continuum spectrum of the variable component
corresponds to a power law with a constant slope of -1.6, while in the 2.4-10
keV X-ray band it varies in slope from -1.1 to -1.6. The steepest X-ray
spectrum occurs at a flux minimum. During a decline in flux from maximum in
late 2006, the optical and 43 GHz core polarization vectors rotate by ~300
degrees. The continuum spectrum agrees with steady injection of relativistic
electrons with a power-law energy distribution of slope -3.2 that is steepened
to -4.2 at high energies by radiative losses. The X-ray emission at flux
minimum comes most likely from a new component that starts in an upstream
section of the jet where inverse Compton scattering of seed photons from
outside the jet is important. The rotation of the polarization vector implies
that the jet contains a helical magnetic field that extends ~20 pc past the 43
GHz core.Comment: 12 pages, aa.cls style; accepted for publication in A&
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Spatially resolved instability measurements with a heavy ion beam probe
A heavy ion beam probe was used to make simultaneous measurements of the amplitude and phase of both density and space potential fluctuations in an energetic arc plasma. Detailed comparison with theoretical predictions identifies a 70 KHz coherent oscillation as a Kelvin-Helmholtz instability localized to a region of strong fluid shear. (auth
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Density-space potential phase difference in a Kelvin--Helmholtz instability
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Advances in electrostatic energy analyzers for ion beam probe diagnostic systems
How well do state-of-the-art Atmosphere-Ocean general circulation models reproduce atmospheric teleconnection patterns?
This article evaluates the ability of state-of-the-art climate models to reproduce the low-frequency variability of the mid-tropospheric winter flow of the Northern Hemisphere in terms of atmospheric teleconnection patterns. Therefore, multi-model simulations for present-day conditions, performed for the 4th assessment report of the Intergovernmental Panel on Climate Change, have been analysed and compared with re-analysis data sets. The spatial patterns of atmospheric teleconnections are reproduced reasonably by most of the models. The comparison of coupled with atmosphere-only runs confirmed that a better representation of the forcing by sea surface temperatures has the potential to slightly improve the representation of only wave train-like patterns. Due to internally generated climate variability, the models are not able to reproduce the observed temporal behaviour. Insights into the dynamical reasons for the limited skill of climate models in reproducing teleconnections have been obtained by studying the relation between major teleconnections and zonal wind variability patterns. About half of the models are able to reproduce the observed relationship. For these cases, the quality of simulated teleconnection patterns is largely determined by the quality of zonal wind variability patterns. Therefore, improvements of simulated eddy-mean flow interaction have the potential to improve the atmospheric teleconnections