7,447 research outputs found
X-rays from accretion shocks in T Tauri stars: The case of BP Tau
We present an XMM-Newton observation of the classical T Tauri star BP Tau. In
the XMM-Newton RGS spectrum the O {\sc vii} triplet is clearly detected with a
very weak forbidden line indicating high plasma densities and/or a high UV flux
environment. At the same time concurrent UV data point to a small hot spot
filling factor suggesting an accretion funnel shock as the site of the X-ray
and UV emission. Together with the X-ray data on TW Hya these new observations
suggest such funnels to be a general feature in classical T Tauri stars.Comment: 4 pages, 4 figures, accepted by A&
Accretion, disks, and magnetic activity in the TW Hya association
We present new photometric and spectroscopic data for the M-type members of
the TW Hya association with the aim of a comprehensive study of accretion,
disks and magnetic activity at the critical age of ~10 Myr where circumstellar
matter disappears.Comment: 4 pages, to appear in Proceedings IAU Symposium No. 314, Young Stars
& Planets Near the Sun, 201
Fast computation of MadGraph amplitudes on graphics processing unit (GPU)
Continuing our previous studies on QED and QCD processes, we use the graphics
processing unit (GPU) for fast calculations of helicity amplitudes for general
Standard Model (SM) processes. Additional HEGET codes to handle all SM
interactions are introduced, as well assthe program MG2CUDA that converts
arbitrary MadGraph generated HELAS amplitudess(FORTRAN) into HEGET codes in
CUDA. We test all the codes by comparing amplitudes and cross sections for
multi-jet srocesses at the LHC associated with production of single and double
weak bosonss a top-quark pair, Higgs boson plus a weak boson or a top-quark
pair, and multisle Higgs bosons via weak-boson fusion, where all the heavy
particles are allowes to decay into light quarks and leptons with full spin
correlations. All the helicity amplitudes computed by HEGET are found to agree
with those comsuted by HELAS within the expected numerical accuracy, and the
cross sections obsained by gBASES, a GPU version of the Monte Carlo integration
program, agree wish those obtained by BASES (FORTRAN), as well as those
obtained by MadGraph. The performance of GPU was over a factor of 10 faster
than CPU for all processes except those with the highest number of jets.Comment: 37 pages, 12 figure
X-ray accretion signatures in the close CTTS binary V4046 Sgr
We present Chandra HETGS observations of the classical T Tauri star (CTTS)
V4046 Sgr. The He-like triplets of O VII, Ne IX, and Si XIII are clearly
detected. Similar to the CTTS TW Hya and BP Tau, the forbidden lines of O VII
and Ne IX are weak compared to the intercombination line, indicating high
plasma densities in the X-ray emitting regions. The Si XIII triplet, however,
is within the low-density limit, in agreement with the predictions of the
accretion funnel infall model with an additional stellar corona. V4046 Sgr is
the first close binary exhibiting these features. Together with previous
high-resolution X-ray data on TW Hya and BP Tau, and in contrast to T Tau, now
three out of four CTTS show evidence of accretion funnels.Comment: 5 pages, 5 figure
New Techniques in the Search for Z' Bosons and Other Neutral Resonances
The search for neutral resonances at the energy frontier has a long and
illustrious history, resulting in multiple discoveries. The canonical search
scans the reconstructed invariant mass distribution of identified fermion
pairs. Two recent analyses from the CDF experiment at the Fermilab Tevatron
have applied novel methods to resonance searches. One analysis uses simulated
templates to fit the inverse mass distribution of muon pairs, a quantity with
approximately constant resolution for momenta measured with a tracking
detector. The other analysis measures the angular distribution of electron
pairs as a function of dielectron mass, gaining sensitivity over a probe of the
mass spectrum alone. After reviewing several models that predict new neutral
resonances, we discuss these CDF analyses and potential future applications
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