856 research outputs found
Tomographic Simulations of Accretion Disks in Cataclysmic Variables - Flickering and Wind
Both continuum and emission line flickering are phenomena directly associated
with the mass accretion process. In this work we simulate accretion disk
Doppler maps including the effects of winds and flickering flares. Synthetic
flickering Doppler maps are calculated and the effect of the flickering
parameters on the maps is explored. Jets and winds occur in many astrophysical
objects where accretion disks are present. Jets are generally absent among the
cataclysmic variables (CVs), but there is evidence of mass loss by wind in many
objects. CVs are ideal objects to study accretion disks and consequently to
study the wind associated with these disks. We also present simulations of
accretion disks including the presence of a wind with orbital phase resolution.
Synthetic H-alpha line profiles in the optical region are obtained and their
corresponding Doppler maps are calculated. The effect of the wind simulation
parameters on the wind line profiles is also explored. From this study we
verified that optically thick lines and/or emission by diffuse material into
the primary Roche lobe are necessary to generate single peaked line profiles,
often seen in CVs. The future accounting of these effects is suggested for
interpreting Doppler tomography reconstructions.Comment: 9 pages, 9 figure
An evaluation of Independent Child Trafficking Guardians â early adopter sites
This publication is licensed under the terms of the Open Government Licence v3.0 except where otherwise stated. To view this licence, visit nationalarchives.gov.uk/doc/open-government-licence/version/3This evaluation, conducted by the Home Office and the University of Bedfordshire has assessed the ICTG service in the three original early adopter sites (Greater Manchester, Hampshire, and Wales). The evaluation, conducted across a two-year period from February 2017 â January 2019, considers the original model for the ICTG service which provided one-to-one ICTG support for all children. The overall aim of the evaluation is to answer the question:
What is the âadded valueâ of the ICTG service, and is this different for different groups of children and in different early adopter sites
A Systematic Search for Supersoft X-Ray Sources in the ROSAT All-Sky Survey
We have conducted a systematic search for supersoft X-ray sources using the
ROSAT all-sky survey data. With the optical identification of the selected
sources being almost complete, we discuss the statistics of the various source
classes and their observability. Besides supersoft close binary sources this
search also can be used to estimate the number of isolated neutron stars in the
Galaxy, such as those described by Stocke et al. 1995 and Walter et al. 1996.Comment: 4 pages postscript, Proc. of Workshop on Supersoft X-Ray Sources, to
appear in Lecture Notes in Physics vol. 472 (1996
A far-ultraviolet variable with an 18-minute period in the globular cluster NGC 1851
We present the detection of a variable star with an 18.05 minute period in far-ultraviolet (FUV) images of the globular cluster NGC 1851 taken with the Hubble Space Telescope (HST). A candidate optical counterpart lies on the red horizontal branch or the asymptotic giant branch star of the cluster, but it is statistically possible that this is a chance superposition. This interpretation is supported by optical spectroscopt obtained with HST/STIS: the spectrum contains none of the strong emission lines that would be expected if the object was a symbiotic star (i.e. a compact accretor fed by a giant donor). We therefore consider two other possibilities for the nature of FUV variable: (i) an intermediate polar (i.e. a compact binary containing an accreting magnetic white dwarf), or (ii) an AM CVn star (i.e. an interacting double-degenerate system). In the intermediate polar scenario, the object is expected to be an X-ray source. However, no X-rays are detected at its location in ? 65 ksec of Chandra imaging, which limits the X-ray luminosity to LX ? 1032 erg s?1. We therefore favour the AM CVn interpretation, but a FUV spectrum is needed to distinguish conclusively between the two possibilities. If the object is an AM CVn binary, it would be the first such system known in any globular cluster
The long-term X-ray lightcurve of RX J0527.8--6954
Supersoft X-ray sources are commonly believed to be stably burning white
dwarfs. However, the observations of some supersoft sources show dramatic
variability of their X-ray flux on timescales ranging from days to years. Here,
we present further observational data of the supersoft X-ray source RX
J0527.8--6954 exhibiting a continuous decline over the past 5 yrs. With no
clear trend of a concordant temperature decrease this might suggest a
evolutionary scenario where the WD leaves the steady burning branch and the
combined effect of reduced luminosity and cooling at constant radius produces
the observed effect.Comment: 6 pages LATEX (with A&A style macro l-aa.tex) including 1 postscript
figure (using psfig.tex) accepted for publication in Astron. Astrophy
The 3-3-1 model with S_4 flavor symmetry
We construct a 3-3-1 model based on family symmetry S_4 responsible for the
neutrino and quark masses. The tribimaximal neutrino mixing and the diagonal
quark mixing have been obtained. The new lepton charge \mathcal{L} related to
the ordinary lepton charge L and a SU(3) charge by L=2/\sqrt{3} T_8+\mathcal{L}
and the lepton parity P_l=(-)^L known as a residual symmetry of L have been
introduced which provide insights in this kind of model. The expected vacuum
alignments resulting in potential minimization can origin from appropriate
violation terms of S_4 and \mathcal{L}. The smallness of seesaw contributions
can be explained from the existence of such terms too. If P_l is not broken by
the vacuum values of the scalar fields, there is no mixing between the exotic
and the ordinary quarks at the tree level.Comment: 20 pages, revised versio
The Energy of Regular Black Hole in General Relativity Coupled to Nonlinear Electrodynamics
According to the Einstein, Weinberg, and M{\o}ller energy-momentum complexes,
we evaluate the energy distribution of the singularity-free solution of the
Einstein field equations coupled to a suitable nonlinear electrodynamics
suggested by Ay\'{o}n-Beato and Garc\'{i}a. The results show that the energy
associated with the definitions of Einstein and Weinberg are the same, but
M{\o}ller not. Using the power series expansion, we find out that the first two
terms in the expression are the same as the energy distributions of the
Reissner-Nordstr\"{o}m solution, and the third term could be used to survey the
factualness between numerous solutions of the Einstein field eqautions coupled
to a nonlinear electrodynamics.Comment: 11 page
New evidence for strong nonthermal effects in Tycho's supernova remnant
For the case of Tycho's supernova remnant (SNR) we present the relation
between the blast wave and contact discontinuity radii calculated within the
nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is
demonstrated that these radii are confirmed by recently published Chandra
measurements which show that the observed contact discontinuity radius is so
close to the shock radius that it can only be explained by efficient CR
acceleration which in turn makes the medium more compressible. Together with
the recently determined new value erg of the SN
explosion energy this also confirms our previous conclusion that a TeV
gamma-ray flux of erg/(cms) is to be expected from
Tycho's SNR. Chandra measurements and the HEGRA upper limit of the TeV
gamma-ray flux together limit the source distance to kpc.Comment: 5 pages, 4 figures. Accepted for publication in Astrophysics and
Space Science, Proc. of "The Multi-Messenger Approach to High-Energy
Gamma-ray Sources (Third Workshop on the Nature of Unidentified High-Energy
Sources)", Barcelona, July 4-7, 200
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