24,171 research outputs found
Observational evidence for the shrinking of bright maser spots
The nature of maser emission means that the apparent angular size of an
individual maser spot is determined by the amplification process as well as by
the instrinsic size of the emitting cloud. Highly sensitive MERLIN radio
interferometry images spatially and spectrally resolve water maser clouds
around evolved stars. We measured the properties of clouds around the red
supergiant S Per and the AGB stars IK Tau, RT Vir, U Her and U Ori, to test
maser beaming theory. Spherical clouds are expected to produce an inverse
relationship between maser intensity and apparent size, which would not be seen
from cylindrical or slab-like regions. We analysed the maser properties, in
order to estimate the saturation state, and investigated the variation of
observed spot size with intensity and across the spectral line profiles.
Circumstellar masers emanate from discrete clouds from about one to 20 AU in
diameter depending on the star. Most of the maser features have negative
excitation temperatures close to zero and modest optical depths, showing that
they are mainly unsaturated. Around S Per and (at most epochs) RT Vir and IK
Tau, the maser component size shrinks with increasing intensity. In contrast,
the masers around U Ori and U Her tend to increase in size, with a larger
scatter. The water masers from S Per, RT Vir and IK Tau are mainly beamed into
spots with an observed angular size much smaller than the emitting clouds and
smallest of all at the line peaks. This suggests that the masers are
amplification-bounded, emanating from approximately spherical clouds. Many of
the masers around U Her and U Ori have apparent sizes which are more similar to
the emitting clouds and have less or no dependence on intensity, suggesting
that these masers are matter-bounded. This is consistent with an origin in
flattened clouds and these two stars have shown other behaviour indicating the
presence of shocks.Comment: 17 pages, 26 figure files, accepted by A&A 2010 Oct 2
Magnetic field in Cepheus A as deduced from OH maser polarimetric observations
We present the results of MERLIN polarization mapping of OH masers at 1665
and 1667 MHz towards the Cepheus A star-forming region. The maser emission is
spread over a region of 6 arcsec by 10 arcsec, twice the extent previously
detected. In contrast to the 22 GHz water masers, the OH masers associated with
H II regions show neither clear velocity gradients nor regular structures. We
identified ten Zeeman pairs which imply a magnetic field strength along the
line-of-sight from -17.3 to +12.7 mG. The magnetic field is organised on the
arcsecond scale, pointing towards us in the west and away from us in the east
side. The linearly polarized components, detected for the first time, show
regularities in the polarization position angles depending on their position.
The electric vectors of OH masers observed towards the outer parts of H II
regions are consistent with the interstellar magnetic field orientation, while
those seen towards the centres of H II regions are parallel to the radio-jets.
A Zeeman quartet inside a southern H II region has now been monitored for 25
years; we confirm that the magnetic field decays monotonically over that
period.Comment: 10 pages, 6 figures,accepted for publication in MNRA
Polarization morphology of SiO masers in the circumstellar envelope of the AGB star R Cassiopeiae
Silicon monoxide maser emission has been detected in the circumstellar
envelopes of many evolved stars in various vibrationally-excited rotational
transitions. It is considered a good tracer of the wind dynamics close to the
photosphere of the star. We have investigated the polarization morphology in
the circumstellar envelope of an AGB star, R Cas. We mapped the linear and
circular polarization of SiO masers in the v=1, J=1-0 transition. The linear
polarization is typically a few tens of percent while the circular polarization
is a few percent. The fractional polarization tends to be higher for emission
of lower total intensity. We found that, in some isolated features the
fractional linear polarization appears to exceed 100%. We found the Faraday
rotation is not negligible but is ~15 deg., which could produce small scale
structure in polarized emission whilst total intensity is smoother and partly
resolved out. The polarization angles vary considerably from feature to feature
but there is a tendency to favour the directions parallel or perpendicular to
the radial direction with respect to the star. In some features, the
polarization angle abruptly flips 90 deg. We found that our data are in the
regime where the model of Goldreich et al (1973) can be applied and the
polarization angle flip is caused when the magnetic field is at close to 55
deg. to the line of sight. The polarization angle configuration is consistent
with a radial magnetic field although other configurations are not excluded.Comment: 14 pages, 15 figures. Accepted for publication in MNRA
A projection method for statics and dynamics of lattice spin systems
A method based on Monte Carlo sampling of the probability flows projected
onto the subspace of one or more slow variables is proposed for investigation
of dynamic and static properties of lattice spin systems. We illustrate the
method by applying it, with projection onto the order-parameter subspace, to
the three-dimensional 3-state Potts model in equilibrium and to metastable
decay in a three-dimensional 3-state kinetic Potts model.Comment: 4 pages, 3 figures, RevTex, final version to appear in Phys. Rev.
Let
AGN and starbursts at high redshift: High resolution EVN radio observations of the Hubble Deep Field
We present deep, wide-field European VLBI Network (EVN) 1.6 GHz observations
of the Hubble Deep Field (HDF) region with a resolution of 0.025 arcseconds.
Above the 210 microJy/beam (5sigma) detection level, the EVN clearly detects
two radio sources in a field that encompasses the HDF and part of the Hubble
Flanking Fields (HFF). The sources detected are: VLA J123644+621133 (a z=1.013,
low-luminosity FR-I radio source located within the HDF itself) and VLA
J123642+621331 (a dust enshrouded, optically faint, z=4.424 starburst system).
A third radio source, J123646+621404, is detected at the 4sigma level. The VLBI
detections of all three sources suggest that most of the radio emission of
these particular sources (including the dusty starburst) is generated by an
embedded AGN.Comment: 4 pages, 1 figure; Accepted by Astron. & Astrophys Letters ... See
http://www.nfra.nl/~mag/hdf_evn.htm
On the edge of a new frontier: Is gerontological social work in the UK ready to meet twenty-first-century challenges?
This article is available open access through the publisher’s website. Copyright @ 2013 The Authors.This article explores the readiness of gerontological social work in the UK for meeting the challenges of an ageing society by investigating the focus on work with older people in social work education and the scope of gerontological social work research. The discussion draws on findings from two exploratory studies: a survey of qualifying master's programmes in England and a survey of the content relating to older people over a six-year period in four leading UK social work journals. The evidence from master's programmes suggests widespread neglect of ageing in teaching content and practice learning. Social work journals present a more nuanced picture. Older people emerge within coverage of generic policy issues for adults, such as personalisation and safeguarding, and there is good evidence of the complexity of need in late life. However, there is little attention to effective social work interventions, with an increasingly diverse older population, or to the quality of gerontological social work education. The case is made for infusing content on older people throughout the social work curriculum, for extending practice learning opportunities in social work with older people and for increasing the volume and reporting of gerontological social work research.Brunel Institute for Ageing Studie
The 43GHz SiO maser in the circumstellar envelope of the AGB star R Cassiopeiae
We present multi-epoch, total intensity, high-resolution images of 43GHz,
v=1, J=1-0 SiO maser emission toward the Mira variable R Cas. In total we have
23 epochs of data for R Cas at approximate monthly intervals over an optical
pulsation phase range from 0.158 to 1.78. These maps show a ring-like
distribution of the maser features in a shell, which is assumed to be centred
on the star at a radius of 1.6 to 2.3 times the stellar radii. It is clear from
these images that the maser emission is significantly extended around the star.
At some epochs a faint outer arc can be seen at 2.2 stellar radii. The
intensity of the emission waxes and wanes during the stellar phase. Some maser
features are seen infalling as well as outflowing. We have made initial
comparisons of our data with models by Gray et. al. (2009).Comment: 12 pages, 14 figure
Clustering on very small scales from a large sample of confirmed quasar pairs: Does quasar clustering track from Mpc to kpc scales?
We present the most precise estimate to date of the clustering of quasars on
very small scales, based on a sample of 47 binary quasars with magnitudes of
and proper transverse separations of \,kpc. Our
sample of binary quasars, which is about 6 times larger than any previous
spectroscopically confirmed sample on these scales, is targeted using a Kernel
Density Estimation technique (KDE) applied to Sloan Digital Sky Survey (SDSS)
imaging over most of the SDSS area. Our sample is "complete" in that all of the
KDE target pairs with \,kpc in our area
of interest have been spectroscopically confirmed from a combination of
previous surveys and our own long-slit observational campaign. We catalogue 230
candidate quasar pairs with angular separations of <8\arcsec, from which our
binary quasars were identified. We determine the projected correlation function
of quasars () in four bins of proper transverse scale over the
range \,kpc. The implied small-scale
quasar clustering amplitude from the projected correlation function, integrated
across our entire redshift range, is at \,kpc. Our sample is the first spectroscopically confirmed sample of
quasar pairs that is sufficiently large to study how quasar clustering evolves
with redshift at kpc. We find that empirical descriptions of
how quasar clustering evolves with redshift at Mpc also
adequately describe the evolution of quasar clustering at
kpc.Comment: 16 pages, 8 figures, 6 tables, Accepted for publication in MNRA
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