58,780 research outputs found

    Discovery of Two Relativistic Neutron Star-White Dwarf Binaries

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    We have discovered two recycled pulsars in relativistic orbits as part of the first high-frequency survey of intermediate Galactic latitudes. PSR J1157-5112 is a 44 ms pulsar and the first recycled pulsar with an ultra-massive (M > 1.14 Mo) white dwarf companion. Millisecond pulsar J1757-5322 is a relativistic circular-orbit system which will coalesce due to the emission of gravitational radiation in less than 9.5 Gyr. Of the ~40 known circular orbit pulsars, J1757-5322 and J1157-5112 have the highest projected orbital velocities. There are now three local neutron-star/white-dwarf binaries that will coalesce in less than a Hubble time, implying a large coalescence rate for these objects in the local Universe. Systems such as J1141-6545 (Kaspi et al. 2000) are potential gamma-ray burst progenitors and dominate the coalescence rate, whilst lighter systems make excellent progenitors of millisecond pulsars with planetary or ultra-low mass companions.Comment: 4 pages, to appear in ApJ Letters. Uses aastex v 5.0, emulateapj5.sty, apjfonts.st

    Humanitarian aid as an integral part of the European Union's external action: the challenge of reconciling coherence and independence

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    The article focuses on the European Union's (EU) humanitarian aid policy. It addresses the challenge for the EU to deliver independent humanitarian aid while simultaneously seeking to establish more coherence between its external policies. The article examines how the EU tries to reconcile these potentially conflicting policy goals, both de jure and in practice. Empirically, it explores the interaction between EU humanitarian aid and development cooperation, the Common Foreign and Security Policy, and trade policy. While the independence of the humanitarian aid delivery is, for the most part, not being undermined, it remains difficult to establish positive synergies with other external policies because of institutional hurdles and legal constraints, as well as political obstacles and operational incompatibilities

    Orbital dynamics of Cygnus X-3

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    Orbital-phased-resolved infrared spectra of Cygnus X-3 in outburst and quiescence, including tomographic analysis, are presented. We confirm the phasing of broad HeII and NV lines in quiescence, such that maximum blue shift corresponds to the X-ray minimum at phase = 0.00 +/- 0.04. In outburst, double-peaked HeI structures show a similar phasing with two significant differences: (a) although varying in relative strength, there is continuous line emission in blue and red peaks around the orbit, and (b) an absorption component, ~1/4 of an orbit out of phase with the emission features, is discerned. Doppler tomograms of the double-peaked profiles are consistent with a disk-wind geometry, rotating at velocities of 1000 km/s. Regrettably, the tomography algorithm will produce a similar ring structure from alternative line sources if contaminated by overlying P Cygni profiles. This is certainly the case in the strong 2.0587 micron HeI line, leading to an ambiguous solution for the nature of double-peaked emission. The absorption feature, detected 1/4 of an orbit out of phase with the emission features, is consistent with an origin in the He star wind and yields for the first time a plausible radial velocity curve for the system. We directly derive the mass function of the system, 0.027 M_sun. If we assume a neutron star accretor and adopt a high orbital inclination, i > 60 degrees, we obtain a mass range for the He star of 5 M_sun < M_WR < 11 M_sun. Alternatively if the compact object is a black hole, we estimate M_BH < 10 M_sun. We discuss the implications of these masses for the nature and size of the binary system.Comment: Accepted for publication in ApJ main journa

    Better Nonlinear Models from Noisy Data: Attractors with Maximum Likelihood

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    A new approach to nonlinear modelling is presented which, by incorporating the global behaviour of the model, lifts shortcomings of both least squares and total least squares parameter estimates. Although ubiquitous in practice, a least squares approach is fundamentally flawed in that it assumes independent, normally distributed (IND) forecast errors: nonlinear models will not yield IND errors even if the noise is IND. A new cost function is obtained via the maximum likelihood principle; superior results are illustrated both for small data sets and infinitely long data streams.Comment: RevTex, 11 pages, 4 figure

    A two-parameter random walk with approximate exponential probability distribution

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    We study a non-Markovian random walk in dimension 1. It depends on two parameters eps_r and eps_l, the probabilities to go straight on when walking to the right, respectively to the left. The position x of the walk after n steps and the number of reversals of direction k are used to estimate eps_r and eps_l. We calculate the joint probability distribution p_n(x,k) in closed form and show that, approximately, it belongs to the exponential family.Comment: 12 pages, updated reference to companion paper cond-mat/060126

    Internal Migration and Regional Population Dynamics in Europe: Netherlands Case Study

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    This report summarises the presentations made and discussions held at the Second of the ESRC/JISC Workshops Planning for the 2001 Census. The report presents views of expert census users and summarises the recommendations to ESRC and JISC about what kinds of data from the 2001 Census should be requested from the UK Census Offices. The Workshops are supported by ESRC Award H507265031. The Census of Population is a very large exercise in data collection and processing. In 2001 some 25 million households in the United Kingdom will be contacted and asked to provide answers to a simple questionnaire of 25 to 30 questions. Such a task is likely to cost £125-150 millions to the Census Offices. Purchase of the data for academic research purposes is likely to cost ESRC and JISC some £1.5 to £2 millions directly and an equivalent amount indirectly on support over the following decade. It is therefore essential that the Population Census is very carefully planned beforehand and that the greatest possible value is extracted from the data collected. This edited collection of papers reports on presentations and discussions in the Fourth and Final Workshop in the series Workshops Planning for the 2001 Census - Determining Academic Community Needs and Strategy. The Fourth Workshop was entitled The 2001 Census: What do we really really want?. The aim was to gather together and summarise the principal recommendations of the First (Geography), Second (Interfaces) and Third (Special Data Sets) Workshops. The Workshop was twinned with another on The One Number Census: A Research Workshop, organised by Ludi Simpson. The One Number Census project is a major undertaking by the Census Offices to deal with anticipated underenumeration by estimating how many households and people are missed by the standard enumeration. Part 1 of the report on Look Up Tables and Area Statistics contains chapters by David Martin on the output geography proposals for 2001, by Seraphim Alvanides and Stan Openshaw on further developments to the methods being used to define output areas and by Bob Barr on what the Look Up Tables associated with the 2001 Census should be like. These chapters contain key recommendations on census output geography. Part 2 of the report puts forward recommendations for the preparation of Microdata - Samples of Anonymised Records and Longitudinal Data from the 2001 Census. Angela Dale summarises the conclusions of the SARs Sub-Group of the Census Offices' Output Working Group. Brian Dodgeon and Heather Joshi document the essential features of the 2001 Census Link to the Longitudinal Study and make a final plea for some new questions. Part 3 of the report reviews proposals for the improvement of Interaction Statistics from the 2001 UK Census. Paul Boyle and Phil Rees make radical proposals for revamping the provision of Migration Statistics. Martin Frost concentrates on ways of improving the accuracy of the Workplace Statistics. The fourth part of the report gathers together recommendations about information technology interfaces to census data, arguing that the tools and infrastructure are now in place to make networked and standalone access to the different types of data so much easier for the new user. Donald Morse and Alistair Towers review what interfaces to boundary data should look like. James Harris argues for the development of interfaces based on general data standards and the Web to access census statistics. Oliver Duke-Williams outlines how complex migration statistics can be presented for access in a simpler and easier to use interface. Ian Turton identifies how current software developments in Java programming will make possible delivering easy to use interfaces to microdata very simple. Finally, Paul Williamson describes a design of a data dictionary for all census data sets. In Part 5, recommendations are summarised. Phil Rees reports on the views of 140 respondents drawn from the different corners of the academic community. The final pages try to draw out some general points from the very large number of recommendations made in the Fourth Workshop

    Hubble Tarantula Treasury Project: Unraveling Tarantula's Web. II. Optical and Near Infrared Star Formation History of the Starburst Cluster NGC 2070 in 30 Doradus

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    We present a study of the recent star formation of 30 Doradus in the Large Magellanic Cloud (LMC) using the panchromatic imaging survey Hubble Tarantula Treasury Project (HTTP). In this paper we focus on the stars within 20 pc of the center of the massive ionizing cluster of 30 Doradus, NGC 2070. We recovered the star formation history by comparing deep optical and NIR color-magnitude diagrams (CMDs) with state-of-the-art synthetic CMDs generated with the latest PARSEC models, which include all stellar phases from pre-main sequence to post- main sequence. For the first time in this region we are able to measure the star formation using intermediate and low mass stars simultaneously. Our results suggest that NGC2070 experienced a prolonged activity. In particular, we find that the star formation in the region: i) exceeded the average LMC rate ~ 20 Myr ago; ii) accelerated dramatically ~ 7 Myr ago; and iii) reached a peak value 1-3 Myr ago. We did not find significant deviations from a Kroupa initial mass function down to 0.5 Msun. The average internal reddening E(B-V) is found to be between 0.3 and 0.4 mag.Comment: Submitted to Ap

    Observed Consequences of Presupernova Instability in Very Massive Stars

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    This chapter concentrates on the deaths of very massive stars, the events leading up to their deaths, and how mass loss affects the resulting death. The previous three chapters emphasized the theory of wind mass loss, eruptions, and core collapse physics, but here we emphasize mainly the observational properties of the resulting death throes. Mass loss through winds, eruptions, and interacting binaries largely determines the wide variety of different types of supernovae that are observed, as well as the circumstellar environments into which the supernova blast waves expand. Connecting these observed properties of the explosions to the initial masses of their progenitor stars is, however, an enduring challenge and is especially difficult for very massive stars. Superluminous supernovae, pair instability supernovae, gamma ray bursts, and "failed" supernovae are all end fates that have been proposed for very massive stars, but the range of initial masses or other conditions leading to each of these (if they actually occur) are still very certain. Extrapolating to infer the role of very massive stars in the early universe is essentially unencumbered by observational constraints and still quite dicey.Comment: 39 pages, 5 figures, to appear as chapter in the book "Very Massive Stars in the Local Universe", ed. J. Vin
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