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

MERLIN imaging of the maser flare in Markarian 348

MERLIN images of Mrk 348 at 22 GHz show water maser emission at 0.02 - 0.11 Jy, within approximately 0.8 pc of the nucleus. This is the first direct confirmation that molecular material exists close to the Seyfert 2 nucleus. Mrk 348 was observed in 2000 May one month after Falcke et al. (2000) first identified the maser in single-dish spectra. The peak maser flux density has increased about threefold. The masing region is < 0.6 pc in radius. The flux density of radio continuum emission from the core has been rising for about 2 years. The maser-core separation is barely resolved but at the 3 sigma significance level they are not coincident along the line of sight. The masers lie in the direction of the northern radio lobes and probably emanate from material shocked by a jet with velocity close to c. The correlation between the radio continuum increase and maser flare is explained as arising from high level nuclear activity through a common excitation mechanism although direct maser amplification of the core by masers tracing a Keplerian disc is not completely ruled out.Comment: Accepted by MNRAS Letters, 5 pages, 3 figures, corrections in text and figur

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