858 research outputs found
Sedimentary heterogeneity and petrophysical characterization of Barremian tsunami and barrier island/inlet deposits: The Aliaga outcrop as a reservoir analogue (Galve sub-basin, eastern Spain)
The present study examined two sandstone deposits in the Aliaga outcrop as a reservoir analogue over a distance of 200-m-long and attempted to establish a correlation between sand facies and the petrophysical properties of the sandstones in order to investigate the reservoir heterogeneity. The Aliaga reservoir analogue represents the upper part of Camarillas Fm., deposited during the Barremian synrift phase of the Galve sub-basin (Iberian Basin, Spain). It is characterized by a transitional sedimentary interval from sandy-dominant deposits to carbonate-dominant deposits, which were deposited under the same palaeoenvironmental conditions (in relation to systems of back-barrier sedimentation).
The description of the Aliaga outcrop provided here consists of lithological descriptions of two sandstone deposits: a tsunami and a barrier island/inlet, at both mesoscopic (decimetres to tens of metres) and microscopic scales (millimetres to centimetres). Both deposits recognized at the basin scale were described in terms of sand grain size, sand sorting and cementation; further cores were drilled along outcrop to collect samples for porosity and permeability measurements.
Both sandstone reservoirs are the result of different sedimentary processes that determined facies characteristics, as the different petrophysical properties observed in these deposits. Consequently, the sedimentary process controls the heterogeneity of the sandstones facies and thus, the sand heterogeneity controls the distribution of the petrophysical properties. The classification of sand facies in terms of sand sorting seems to be more appropriate for describing sand heterogeneity; accordingly, petrophysical parameters in both deposits were also influenced by sand sorting.
The sand facies and petrophysics heterogeneity of the described deposits can be hierarchically ordered. First-order heterogeneity is related to the basin scale, second-order heterogeneity is related to genesis and the conditions of sediment deposition, and third-order heterogeneity is related to synsedimentary faults and/or post-sedimentation events.This research is a contribution to the project: Análisis de Cuencas Sedimentarias Continentales, of the Gobierno de Aragón, the Análisis de Cuencas Sedimentarias Group of the UCM-CAM, and the projects CGL2011-23717 (Ministerio de Ciencia e Innovación of the Spanish Government and FEDER) and UZ2015-CIE-10 (University of Zaragoza). Additional financial support was provided by a Cnpq (Conselho Nacional de Pesquisa e Desenvolvimento Tecnologico, Brasil) Research Grant (200147/2011-0) and an IAS Schema 1st session 2014 Postgraduate Grant to F. Veloso.Peer reviewe
Shallow extra mixing in solar twins inferred from Be abundances
Lithium and beryllium are destroyed at different temperatures in stellar
interiors. As such, their relative abundances offer excellent probes of the
nature and extent of mixing processes within and below the convection zone. We
determine Be abundances for a sample of eight solar twins for which Li
abundances have previously been determined. The analyzed solar twins span a
very wide range of age, 0.5-8.2 Gyr, which enables us to study secular
evolution of Li and Be depletion. We gathered high-quality UVES/VLT spectra and
obtained Be abundances by spectral synthesis of the Be II 313 nm doublet. The
derived beryllium abundances exhibit no significant variation with age. The
more fragile Li, however, exhibits a monotonically decreasing abundance with
increasing age. Therefore, relatively shallow extra mixing below the convection
zone is necessary to simultaneously account for the observed Li and Be behavior
in the Sun and solar twins
New Indicators for AGN Power: The Correlation Between [O IV] lambda 25.89 micron and Hard X-ray Luminosity for Nearby Seyfert Galaxies
We have studied the relationship between the [O IV] lambda 25.89 micron
emission line luminosities, obtained from Spitzer spectra, the X-ray continua
in the 2-10 keV band, primarily from ASCA, and the 14-195 keV band obtained
with the SWIFT/Burst Alert Telescope (BAT), for a sample of nearby (z < 0.08)
Seyfert galaxies. For comparison, we have examined the relationship between the
[O III] 5007, the 2-10 keV and the 14-195 keV luminosities for the same set of
objects. We find that both the [O IV] and [O III] luminosities are
well-correlated with the BAT luminosities. On the other hand, the [O III]
luminosities are better-correlated with 2-10 keV luminosities than are those of
[O IV]. When comparing [O IV] and [O III] luminosities for the different types
of galaxies, we find that the Seyfert 2's have significantly lower [O III] to
[O IV] ratios than the Seyfert 1's. We suggest that this is due to more
reddening of the narrow line region (NLR) of the Seyfert 2's. Assuming Galactic
dust to gas ratios, the average amount of extra reddening corresponds to a
hydrogen column density of ~ few times 10^21 cm^-2, which is a small fraction
of the X-ray absorbing columns in the Seyfert 2's. The combined effects of
reddening and the X-ray absorption are the probable reason why the [O III]
versus 2-10 keV correlation is better than the [O IV] versus 2-10 keV, since
the [O IV] emission line is much less affected by extinction. Overall, we find
the [O IV] to be an accurate and truly isotropic indicator of the power of the
AGN. This suggests that it can be useful in deconvolving the contribution of
the AGN and starburst to the spectrum of Compton-thick and/or X-ray weak
sources.Comment: Accepted for publication in the Astrophysical Journal. 31 pages, 6
figures, 4 table
Uncovering the Spectral Energy Distribution in Active Galaxies Using High Ionization Mid-infrared Emission Lines
The shape of the spectral energy distribution of active galaxies in the
EUV--soft X-ray band (13.6 eV to 1 keV) is uncertain because obscuration by
dust and gas can hamper our view of the continuum. To investigate the shape of
the spectral energy distribution in this energy band, we have generated a set
of photoionization models which reproduce the small dispersion found in
correlations between high-ionization mid-infrared emission lines in a sample of
hard X-ray selected AGN. Our calculations show that a broken power-law
continuum model is sufficient to reproduce the [Ne V]14.32 mm/[NeIII], [Ne
V]24.32mm/[O IV]25.89mm and [O IV] 25.89mm/[Ne III] ratios, and does not
require the addition of a "big bump" EUV model component. We constrain the
EUV--soft X-ray slope, alpha_i, to be between 1.5 -- 2.0 and derive a best fit
of alpha_i ~ 1.9 for Seyfert 1 galaxies, consistent with previous studies of
intermediate redshift quasars. If we assume a blue bump model, most sources in
our sample have derived temperatures between T_{BB}=10^{5.18} K to 10^{5.7} K,
suggesting that the peak of this component spans a large range of energies
extending from ~ lambda 600A to lambda 1900A. In this case, the best fitting
peak energy that matches the mid-infrared line ratios of Seyfert 1 galaxies
occurs between ~ lambda 700--1000A. Despite the fact that our results do not
rule out the presence of an EUV bump, we conclude that our power-law model
produces enough photons with energies > 4 Ry to generate the observed amount of
mid-infrared emission in our sample of BAT AGN.Comment: Accepted for publication in The Astrophysical Journal. 11 Figure
THE CALLOVIAN UNCONFORMITY AND THE OPHIOLITE OBDUCTION ONTO THE PELAGONIAN CARBONATE PLATFORM OF THE INTERNAL HELLENIDES
The carbonate-platform-complex and the oceanic formations of the central Pelagonian zone of the Hellenides evolved in response to a sequence of plate tectonic episodes of ocean spreading, plate convergence and ophiolite obduction. The biostratigraphies of the carbonate platform and the oceanic successions, show that the Triassic-Early Jurassic platform was coeval with an ocean where pillow basalts and radiolarian cherts were being deposited. After convergence began during late Early- Jurassic - Middle Jurassic time, the oceanic leading edge of the Pelagonian plate was subducted beneath the leading edge of the oceanic, overriding plate. The platform subsided while a supra-subduction, volcanic-island-arc evolved. Biostratigraphic and geochemical evidence shows that the platform and the oceanic floor, temporarily became subaerially exposed during Callovian time. This “Callovian event” is suggested to have taken place as oceanic lithosphere first made compressional, tectonic contact with the carbonate platform, initiating a basal detachment fault, along which the platform was thrust upwards. The central Pelagonian zone became an extensive land area that was supplied with laterite from an ophiolite highland. A similar emergence of Vardar ophiolite most likely took place in the Guevgueli area. The Callovian emergence shows that the initial ophiolite obduction onto the platform took place about 25 million years before the final emplacement of the ophiolite during Valanginian time
VLT-UVES abundance analysis of four giants in NGC 6553
Metal-rich globular clusters trace the formation of bulges. Abundance ratios
in the metal-rich globular clusters such as NGC 6553 can constrain the
formation timescale of the Galactic bulge. The purpose of this study is
determine the metallicity and elemental ratios in individual stars of the
metal-rich bulge globular cluster NGC 6553. A detailed abundance analysis of
four giants in NGC 6553 is carried out, based on optical high-resolution
echelle spectra obtained with UVES at the ESO VLT-UT2 Kueyen telescope. A
metallicity [Fe/H]= -0.20 dex is derived, together with -element
enhancement of Mg and Si ([Mg/Fe]=+0.28, [Si/Fe]=+0.21), solar Ca and Ti
([Ca/Fe]=+0.05, [Ti/Fe]=-0.01), and a mild enhancement of the r-process element
Eu with [Eu/Fe] = +0.10. A mean heliocentric radial velocity of -1.86 km
s is measured. We compare our results with previous investigations of
the cluster.Comment: 15 pages, 8 figures, A&A, in pres
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