Keele University

About: Keele University is a education organization based out in Newcastle-under-Lyme, United Kingdom. It is known for research contribution in the topics: Population & Stars. The organization has 11318 authors who have published 26323 publications receiving 894671 citations. The organization is also known as: Keele University.

Evidence for ultra-fast outflows in radio-quiet AGNs: II - detailed photo-ionization modeling of Fe K-shell absorption lines

Abstract: X-ray absorption line spectroscopy has recently shown evidence for previously unknown Ultra-fast Outflows (UFOs) in radio-quiet AGNs. In the previous paper of this series we defined UFOs as those absorbers with an outflow velocity higher than 10,000km/s and assessed the statistical significance of the associated blueshifted FeK absorption lines in a large sample of 42 local radio-quiet AGNs observed with XMM-Newton. In the present paper we report a detailed curve of growth analysis and directly model the FeK absorbers with the Xstar photo-ionization code. We confirm that the frequency of sources in the radio-quiet sample showing UFOs is >35%. The outflow velocity distribution spans from \sim10,000km/s (\sim0.03c) up to \sim100,000km/s (\sim0.3c), with a peak and mean value of \sim42,000km/s (\sim0.14c). The ionization parameter is very high and in the range log\xi 3-6erg s^{-1} cm, with a mean value of log\xi 4.2 erg s^{-1} cm. The associated column densities are also large, in the range N_H\sim10^{22}-10^{24} cm^{-2}, with a mean value of N_H\sim10^{23} cm^{-2}. We discuss and estimate how selection effects, such as those related to the limited instrumental sensitivity at energies above 7keV, may hamper the detection of even higher velocities and higher ionization absorbers. We argue that, overall, these results point to the presence of extremely ionized and possibly almost Compton thick outflowing material in the innermost regions of AGNs. This also suggests that UFOs may potentially play a significant role in the expected cosmological feedback from AGNs and their study can provide important clues on the connection between accretion disks, winds and jets.

Southern Menderes Massif: an incipient metamorphic core complex in western Anatolia, Turkey

Abstract: In the southern sector of the Menderes Massif, north of Selimiye (Milas) augen gneisses interpreted as a deformed peraluminous granite have been dynamothermally metamorphosed and are surrounded by and intrude a regionally metamorphosed Palaeozoic ‘envelope’ The granitic rocks exhibit a moderately-dipping mylonitic foliation and NNE-SSW- trending mineral elongation lineation The progressive deformation of the granitic rocks produces a structural sequence typical of an extensional shear zone marked, from bottom to top, by a very thick extensive zone of mylonites followed in turn by brecciated mylonite and cataclasite The kinematic indicators exhibit a top-to-the south, down-dip sense of shear These structures are attributed to exhumation of the granitic rocks of the massif along a major, south-dipping, normal-sense shear zone that accommodated crustal extension during Late Oligocene collapse of the orogen in western Turkey Thus, the southern Menderes Massif may be interpreted as the exhumed footwall of a major extensional shear zone, and possibly as an incipient core complex

The Gaia-ESO Survey : radial metallicity gradients and age-metallicity relation of stars in the Milky Way disk

Abstract: We study the relationship between age, metallicity, and alpha-enhancement of FGK stars in the Galactic disk. The results are based upon the analysis of high-resolution UVES spectra from the Gaia-ESO large stellar survey. We explore the limitations of the observed dataset, i.e. the accuracy of stellar parameters and the selection effects that are caused by the photometric target preselection. We find that the colour and magnitude cuts in the survey suppress old metal-rich stars and young metal-poor stars. This suppression may be as high as 97% in some regions of the age-metallicity relationship. The dataset consists of 144 stars with a wide range of ages from 0.5 Gyr to 13.5 Gyr, Galactocentric distances from 6 kpc to 9.5 kpc, and vertical distances from the plane 0 9 Gyr is not as small as advocated by some other studies. In agreement with earlier work, we find that radial abundance gradients change as a function of vertical distance from the plane. The [Mg/Fe] gradient steepens and becomes negative. In addition, we show that the inner disk is not only more alpha-rich compared to the outer disk, but also older, as traced independently by the ages and Mg abundances of stars.

Convective-reactive Proton-12C Combustion in Sakurai's Object (V4334 Sagittarii) and Implications for the Evolution and Yields from the First Generations of Stars

Abstract: Depending on mass and metallicity as well as evolutionary phase, stars occasionally experience convectivereactive nucleosynthesis episodes. We specifically investigate the situation when nucleosynthetically unprocessed, H-rich material is convectively mixed with a He-burning zone, for example in convectively unstable shell on top of electron-degenerate cores in AGB stars, young white dwarfs or X-ray bursting neutron stars. Such episodes are frequently encountered in stellar evolution models of stars of extremely low or zero metal content, such as the first stars. We have carried out detailed nucleosynthesis simulations based on stellar evolution models and informed by hydrodynamic simulations. We focus on the convective-reactive episode in the very-late thermal pulse star Sakurai’s object (V4334 Sagittarii). Asplund et al. (1999) determined the abundances of 28 elements, many of which are highly non-solar, ranging from H, He and Li all the way to Ba and La, plus the C isotopic ratio. Our simulations show that the mixing evolution according to standard, one-dimensional stellar evolution models implies neutron densities in the He intershell (. few 10 11 cm -3 ) that are too low to obtain a significant neutron capture nucleosynthesis on the heavy elements. We have carried out 3D hydrodynamic He-shell flash convection simulations in 4 geometry to study the entrainment of H-rich material. Guided by these simulations we assume that the ingestion process of H into the He-shell convection zone leads only after some delay time to a sufficient entropy barrier that splits the convection zone into the original one driven by He-burning and a new one driven by the rapid burning of ingested H. By making such mixing assumptions that are motivated by our hydrodynamic simulations we obtain significantly higher neutron densities ( few 10 15 cm -3 ) and reproduce the key observed abundance trends found in Sakurai’s object. These include an overproduction of Rb, Sr and Y by about 2 orders of magnitude higher than the overproduction of Ba and La. Such a peculiar nucleosynthesis signature is impossible to obtain with the mixing predictions in our one-dimensional stellar evolution models. The simulated Li abundance and the isotopic ratio 12 C/ 13 C are as well in agreement with observations. Details of the observed heavy element abundances can be used as a sensitive diagnostic tool for the neutron density, for the neutron exposure and, in general, for the physics of the convective-reactive phases in stellar evolution. For example, the high elemental ratio Sc/Ca and the high Sc production indicate high neutron densities. The diagnostic value of such abundance markers depends on uncertain nuclear physics input. We determine how our results depend on uncertainties of nuclear reaction rates, for example for the 13 C(; n) 16 O reaction. Subject headings: stars: AGB and post-AGB — stars: abundances — stars: evolution — stars: interior — stars: individual (V4334 Sagittarii) — physical data and processes: hydrodynamics — physical data and processes: nuclear reactions, nucleosynthesis, abundances

Do Board’s Corporate Social Responsibility Strategy and Orientation Influence Environmental Sustainability Disclosure? UK Evidence

Abstract: The environmental implications of corporate economic activities have led to growing demands for firms and their boards to adopt sustainable strategies and to disseminate more useful information about their activities and impacts on environment. This paper investigates the impact of board’s corporate social responsibility (CSR) strategy and orientation on the quantity and quality of environmental sustainability disclosure in UK listed firms. We find that effective board CSR strategy and CSR-oriented directors have a positive and significant impact on the quality of environmental sustainability disclosure, but not on the quantity. Our findings also suggest that the existence of a CSR committee and issuance of a stand-alone CSR report are positively and significantly related to environmental sustainability disclosure. When we distinguish between firms with high and low environmental risk, we find that the board CSR/sustainability practices that affect the quantity (quality) of environmental sustainability disclosure appear to be driven more by highly (lowly) environmentally sensitive firms. These results suggest that the board CSR/sustainability practices play an important role in ensuring a firm’s legitimacy and accountability towards stakeholders. Our findings shed new light on this under-researched area and could be of interest to companies, policy-makers and other stakeholders.