3,759 research outputs found
Sistemas lacustres paleógenos de Mallorca (Mediterráneo Occidental)
Dos importantes sistemas lacustres-palustres se desarrollaron durante el Paleógeno en las Baleares. En el primero de ellos, de edad Bartoniense (Eoceno medio), se formó una importante acumulación de sedimentos carbonatados biogénicos y organógenos (lignitos). La organización megasecuencial de las sucesiones lacustres registra la siguiente evolución del sistema: 1) implantación de los medios lacustres, 2) expansión y relativa profundización, 3) colmatación por progradación de los depósitos de las zonas marginales del sistema sobre las internas y 4) etapa final, dominantemente agradante, con un pronunciado equilibrio entre las tasas de sedimentación y subsidencia. El segundo sistema, de edad oligocena (Estampiense superior- Chatiense), esta constituido por una asociación de depósitos lacustres y palustres relacionados con facies distales de un sistema aluvial. Por ello, el aporte de materiales detriticos finos al sistema lacustre jugó un papel primordial; aunque en las zonas mis protegidas de las cubetas lacustres, la acumulación de carbonatos biogénicos y la de maicriaorginica fue también importante. Su evolución megasecuencial sugiere las siguientes fases: 1) implantación en zonas terminalesdistales del sistema aluvial, 2) expansión e implantación de depocentros carbonatados, y 3) colmatación final relacionada con la progradación de las zonas terminales del sistema aluvial. Ambos sistemas lacustres indican el desarrollo de etapas de estratificación permanente u ocasional de la columna de agua. Ello permitió lapreservación de materia orgánica derivada de macrófitos superiores y de organismos algales y bacterias
Estructura y relleno sedimentario de la semifosa neógena de Vilanova (Garraf, Barcelona)
A joint study involving geological mapping, well subsurface data and gravity modelling has been carried out in the Vilanova half graben in order to define the substralum structure and the character of the sedimentary in fill.The half graben is oriented following a regional ENE-WSW fault direction. Its structure is controlled by normal faults along the NW boundary and by an unconformity in the SE basin boundary. A perpendicular to the main direction fault system, configurate a block shaped hasement. From the residual gravity map a 3D density model, constrained with the depths infered kom bore oles, has been obtained. The sedimentary infill has been divided in four litostratigraphic units. One of them constitutes a marginal complex associated and genetically related with the main faults that bound the basin. The otber three units show a vertical evolution from continental alluvial environrnent at the bottom to marine (littoral and restricted shelf-bay) at tbe top.The paleomastological data allow ps to attribute to the autcropping sedimentary infill a Serravallian age. Nevertheless, an Aquitanian-Early Burdigalian age to the basal conglomeratic unit can't be definitively rejected
VISIR-VLT high resolution study of the extended emission of four obscured post-AGB candidates
The onset of the asymmetry of planetary nebulae (PNe) is expected to occur
during the late Asymptotic Giant Branch (AGB) and early post-AGB phases of low-
and intermediate-mass stars. Among all post-AGB objects, the most heavily
obscured ones might have escaped the selection criteria of previous studies
detecting extreme axysimmetric structures in young PNe. Since the most heavily
obscured post-AGB sources can be expected to descend from the most massive PN
progenitors, these should exhibit clear asymmetric morphologies. We have
obtained VISIR-VLT mid-IR images of four heavily obscured post-AGB objects
barely resolved in previous Spitzer IRAC observations to analyze their
morphology and physical conditions across the mid-IR. The VISIR-VLT images have
been deconvolved, flux calibrated, and used to construct RGB composite pictures
as well as color and optical depth maps that allow us to study the morphology
and physical properties of the extended emission of these sources. We have
detected extended emission from the four objects in our sample and resolved it
into several structural components that are greatly enhanced in the temperature
and optical depth maps. They reveal the presence of asymmetry in three young
PNe (IRAS 15534-5422, IRAS 17009-4154, and IRAS 18454+0001), where the
asymmetries can be associated with dusty torii and slightly bipolar outflows.
The fourth source (IRAS 18229-1127), a possible post-AGB star, is better
described as a rhomboidal detached shell. The heavily obscured sources in our
sample do not show extreme axisymmetric morphologies. This is at odds with the
expectation of highly asymmetrical morphologies in post-AGB sources descending
from massive PN progenitors. The sources presented in this paper may be
sampling critical early phases in the evolution of massive PN progenitors,
before extreme asymmetries develop.Comment: 9 pages, 4 figure
Icnología de vertebrados de la facies Buntsandstein de Mallorca
Se describen, por primera vez en Mallorca, hasta cinco tipos diferentes de icnitas y pistas de vertebrados continentales dentro de las facies cuarzoareniticas y limosas rojas de la facies Buntsandstein del Triásico inferio
Extended X-ray emission from the classic nova DQ Her -- On the possible presence of a magnetized jet
We present an analysis of archival Chandra and XMM-Newton observations of the
magnetically-active cataclysmic variable DQ Her and the shell around it ejected
in a nova event in 1934. A careful revision of the Chandra observations
confirms previous claims on the presence of extended X-ray emission around DQ
Her and reveals that it actually corresponds to a bipolar jet-like structure
extending 32 along a direction from NE to SW. Therefore, this X-ray
emission extends beyond the optical nova shell and is perpendicular to its
major axis. The XMM-Newton observations confirm the presence of the extended
X-ray emission detected by Chandra, suggesting the additional presence of a
diffuse X-ray emission from a hot bubble filling the nova shell. This hot
bubble was very likely produced by the explosion that created the nebular shell
detected in optical images. The bipolar feature can be modelled by the
combination of an optically thin plasma emission component with temperature
K and a power law component with a photon index of
. Its X-ray luminosity in the 0.3 - 5 keV energy range is
erg s, for an electron density
cm and a mass M. We suggest that the X-ray bipolar structure in DQ
Her is a jet and interpret its non-thermal X-ray emission in terms of a
magnetized jet.Comment: 8 pages, 4 figures, 1 table; accepted to MNRA
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