42,425 research outputs found

    Eddington limited starbursts in the central 10pc of AGN, and the Torus in NGC1068

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    We present results from a survey of nearby AGN using the near infrared adaptive optics integral field spectrograph SINFONI. These data enable us to probe the distribution and kinematics of the gas and stars at spatial resolutions as small as 0.085arcsec. We find strong evidence for recent but short lived starbursts residing in very dense nuclear disks. On scales of less than 10pc these would have reached Eddington-limited luminosities when active, perhaps accounting for their short duration. In addition, for NGC1068 at a resolution of 6pc, we present direct observations of molecular gas close around the AGN which we identify with the obscuring torus.Comment: Conference proceedings to appear in "The Central Engine of Active Galactic Nuclei", ed. L. C. Ho and J.-M. Wang (San Francisco: ASP

    Teaching Media Production: Understanding Unconscious Bias in Creative Idea Development

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    Drawing on initial findings based on observations, surveys and interviews with a range of new entrants and established television professionals, carried out during an 18 month period working with a talent development scheme, we discuss the perspectives these findings have given us on teaching practices within our own institutions and how we are seeking to bring these insights into changing these practices. In particular we discuss the way that the presence of unconscious bias and assumed consensus within the idea development process can reinforce structural inequalities, militating against the aims of broadcasters to produce a truly diverse range of programmes. We propose that it is equally important for media educators to be aware of the presence of unconscious bias and of ways of tackling it in relation to creative idea development within the academy. We discuss both the barriers and potential solutions for an inclusive approach to the idea development process

    Recognising and addressing unconscious bias and structural inequalities

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    This article examines the idea development process within the UK television industry and raises the question of who has power and agency within it. Recently, there has been much discussion within the television industry about the commercial and social imperative for greater diversity, inclusion and risk taking in programme making, in order to both represent and appeal to contemporary audiences. However, our research suggests that there is at the same time a sense of disempowerment, a feeling that television culture itself is inhibiting this change and that individuals can do little to influence it. Building on existing research in the creative industries, this case study draws on observations, interviews and surveys carried out within the context of a talent development scheme and wider consultation with television development professionals. We will discuss the reasons for these contradictory currents of feeling, including the ways in which unconscious bias may operate to perpetuate inequalities and exclusions. Our article proposes that recognising and addressing unconscious bias within the idea development process is an important element in the wider process of tackling structural inequality in the television industry through collective action and institutional chang

    Gravitational Radiation From Globular Clusters

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    Space-based gravitational wave detectors will have the ability to observe continuous low frequency gravitational radiation from binary star systems. They can determine the direction to continuous sources with an angular resolution approaching tens of arcminutes. This resolution should be sufficient to identify binary sources as members of some nearby globular clusters. Thus, gravitational radiation can be used to determine the population of hard binaries in globular clusters. For particularly hard binaries, the orbital period may change as a result of gravitational wave emission. If one of these binaries can be identified with a globular cluster, then the distance to that cluster can be determined. Thus, gravitational radiation may provide reddening-independent distance measurements to globular clusters.Comment: 26 pages, 1 figure, LaTeX, uses aasms4.sty, submitted to Ap.

    Are There Magnetars in High Mass X-ray Binaries? The Case of SuperGiant Fast X-Ray Transients

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    In this paper we survey the theory of wind accretion in high mass X-ray binaries hosting a magnetic neutron star and a supergiant companion. We concentrate on the different types of interaction between the inflowing wind matter and the neutron star magnetosphere that are relevant when accretion of matter onto the neutron star surface is largely inhibited; these include the inhibition through the centrifugal and magnetic barriers. Expanding on earlier work, we calculate the expected luminosity for each regime and derive the conditions under which transition from one regime to another can take place. We show that very large luminosity swings (~10^4 or more on time scales as short as hours) can result from transitions across different regimes. The activity displayed by supergiant fast X-ray transients, a recently discovered class of high mass X-ray binaries in our galaxy, has often been interpreted in terms of direct accretion onto a neutron star immersed in an extremely clumpy stellar wind. We show here that the transitions across the magnetic and/or centrifugal barriers can explain the variability properties of these sources as a results of relatively modest variations in the stellar wind velocity and/or density. According to this interpretation we expect that supergiant fast X-ray transients which display very large luminosity swings and host a slowly spinning neutron star are characterized by magnetar-like fields, irrespective of whether the magnetic or the centrifugal barrier applies. Supergiant fast X-ray transients might thus provide a new opportunity to detect and study magnetars in binary systems.Comment: Accepted for publication in ApJ. 16 pages, 6 figure

    Propagation of the First Flames in Type Ia Supernovae

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    We consider the competition of the different physical processes that can affect the evolution of a flame bubble in a Type Ia supernovae -- burning, turbulence and buoyancy. Even in the vigorously turbulent conditions of a convecting white dwarf, thermonuclear burning that begins at a point near the center (within 100 km) of the star is dominated by the spherical laminar expansion of the flame, until the burning region reaches kilometers in size. Consequently flames that ignite in the inner ~20 km promptly burn through the center, and flame bubbles anywhere must grow quite large--indeed, resolvable by large-scale simulations of the global system--for significant motion or deformation occur. As a result, any hot-spot that successfully ignites into a flame can burn a significant amount of white dwarf material. This potentially increases the stochastic nature of the explosion compared to a scenario where a simmering progenitor can have small early hot-spots float harmlessly away. Further, the size where the laminar flame speed dominates other relevant velocities sets a characteristic scale for fragmentation of larger flame structures, as nothing--by definition--can easily break the burning region into smaller volumes. This makes possible the development of semi-analytic descriptions of the earliest phase of the propagation of burning in a Type Ia supernovae, which we present here. Our analysis is supported by fully resolved numerical simulations of flame bubbles.Comment: 33 pages, 14 figures, accepted for publication in Ap

    A photometric analysis of Abell 1689: two-dimensional multi-structure decomposition, morphological classification, and the Fundamental Plane

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    We present a photometric analysis of 65 galaxies in the rich cluster Abell 1689 at z=0.183z=0.183, using the Hubble Space Telescope Advanced Camera for Surveys archive images in the rest-frame VV-band. We perform two-dimensional multi-component photometric decomposition of each galaxy adopting different models of the surface-brightness distribution. We present an accurate morphological classification for each of the sample galaxies. For 50 early-type galaxies, we fit both a de Vaucouleurs and S\'ersic law; S0s are modelled by also including a disc component described by an exponential law. Bars of SB0s are described by the profile of a Ferrers ellipsoid. For the 15 spirals, we model a S\'ersic bulge, exponential disc, and, when required, a Ferrers bar component. We derive the Fundamental Plane by fitting 40 early-type galaxies in the sample, using different surface-brightness distributions. We find that the tightest plane is that derived by S\'ersic bulges. We find that bulges of spirals lie on the same relation. The Fundamental Plane is better defined by the bulges alone rather than the entire galaxies. Comparison with local samples shows both an offset and rotation in the Fundamental Plane of Abell 1689.Comment: 53 pages, 71 figures, MNRAS in pres

    A Radio Determination of the Time of the New Moon

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    The detection of the New Moon at sunset is of importance to communities based on the lunar calendar. This is traditionally undertaken with visual observations. We propose a radio method which allows a higher visibility of the Moon relative to the Sun and consequently gives us the ability to detect the Moon much closer to the Sun than is the case of visual observation. We first compare the relative brightness of the Moon and Sun over a range of possible frequencies and find the range 5--100\,GHz to be suitable. The next consideration is the atmospheric absorption/emission due to water vapour and oxygen as a function of frequency. This is particularly important since the relevant observations are near the horizon. We show that a frequency of ∌10\sim 10 GHz is optimal for this programme. We have designed and constructed a telescope with a FWHM resolution of 0∘ ⁣ ⁣^\circ{}\!\!.6 and low sidelobes to demonstrate the potential of this approach. At the time of the 21 May 2012 New Moon the Sun/Moon brightness temperature ratio was 72.7±2.272.7 \pm 2.2 in agreement with predictions from the literature when combined with the observed sunspot numbers for the day. The Moon would have been readily detectable at ∌2∘\sim 2^{\circ} from the Sun. Our observations at 16\,hr\,36\,min UT indicated that the Moon would have been at closest approach to the Sun 16\,hr\,25\,min earlier; this was the annular solar eclipse of 00\,hr\,00\,min\,UT on 21 May 2012.Comment: 11 pages, 15 figures, accepted for publication in MNRA

    The Planck Surveyor mission: astrophysical prospects

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    Although the Planck Surveyor mission is optimized to map the cosmic microwave background anisotropies, it will also provide extremely valuable information on astrophysical phenomena. We review our present understanding of Galactic and extragalactic foregrounds relevant to the mission and discuss on one side, Planck's impact on the study of their properties and, on the other side, to what extent foreground contamination may affect Planck's ability to accurately determine cosmological parameters. Planck's multifrequency surveys will be unique in their coverage of large areas of the sky (actually, of the full sky); this will extend by two or more orders of magnitude the flux density interval over which mm/sub-mm counts of extragalactic sources can be determined by instruments already available (like SCUBA) or planned for the next decade (like the LSA-MMA or the space mission FIRST), which go much deeper but over very limited areas. Planck will thus provide essential complementary information on the epoch-dependent luminosity functions. Bright radio sources will be studied over a poorly explored frequency range where spectral signatures, essential to understand the physical processes that are going on, show up. The Sunyaev-Zeldovich effect, with its extremely rich information content, will be observed in the direction of a large number of rich clusters of Galaxies. Thanks again to its all sky coverage, Planck will provide unique information on the structure and on the emission properties of the interstellar medium in the Galaxy. At the same time, the foregrounds are unlikely to substantially limit Planck's ability to measure the cosmological signals. Even measurements of polarization of the primordial Cosmic Microwave background fluctuations appear to be feasible.Comment: 20 pages, Latex (use aipproc2.sty, aipproc2.cls, epsfig.sty), 10 PostScript figures; invited review talk, Proc. of the Conference: "3 K Cosmology", Roma, Italy, 5-10 October 1998, AIP Conference Proc, in press Note: Figures 6 and 7 have been replaced by new and correct version
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