570 research outputs found
Estratigrafía del Cretácico inferior continental de la Cordillera Ibérica Central
Continental sedimentation during early Cretaceous in the Central part of the Iberian basin took place in two sedimentary sub-basins, the Oliete and Aguilón sub-basins. The stratigraphic analysis carried out in these units allows us to define new lithostratigraphical units. The biostratigraphy analysis of these units was based on charophytes. The identification of regional unconformities allows to define three depositional sequences. These sequences span from the Valanginian or Hauterivian to the Early Barremian, and may be correlated to sequences K1.2 or K1.3, K1.4 and K1.5 or K1.6 D.S., previously defined by Salas et al. (1991) and Salas & Casas (1993) in the eastem Maestrazgo basin. These results indicate that the stratigraphic record of the central part of the Iberian basin is as completed as that of the margin of the neighbouring Maestrazgo, Aliaga-Peñagolosa and Cameros basins.El Cretácico inferior continental de la Cordillera Ibérica Central está representado en dos subcuencas de sedimentación: las Cubetas de Aguilón y Oliete. Los estudios realizados sobre estos materiales han permitido definir nuevas unidades litoestratigráficas, cuya caracterización bioestratigráfica se realiza a partir de su contenido en carofitas. La identificación de discontinuidades significativas permiten definir tres secuencias de depósito que abarcan el intervalo temporal Valanguniense y/o Hauteriviense-Barremiense inferior y que son correlacionables con las S.D.K1.2 y/o K1.3, K1.4 YK1.5 y/o K1.6 definidas en Salas et al. (1991) y Salas y Casas (1993) para la Cuenca del Maestrazgo. Estos resultados ponen de manifiesto que el registro estratigráfico de la zona central de la Cordillera Ibérica tiene una entidad similar al de los márgenes de las Cuencas del Maestrazgo, Aliaga- Peñagolosa y Cameros
The radius and mass of the close solar twin 18 Sco derived from asteroseismology and interferometry
The growing interest in solar twins is motivated by the possibility of
comparing them directly to the Sun. To carry on this kind of analysis, we need
to know their physical characteristics with precision. Our first objective is
to use asteroseismology and interferometry on the brightest of them: 18 Sco. We
observed the star during 12 nights with HARPS for seismology and used the PAVO
beam-combiner at CHARA for interferometry. An average large frequency
separation Hz and angular and linear radiuses of mas and R were estimated. We used these
values to derive the mass of the star, M.Comment: 5 pages, 5 figure
Observation of interstellar lithium in the low-metallicity Small Magellanic Cloud
The primordial abundances of light elements produced in the standard theory
of Big Bang nucleosynthesis (BBN) depend only on the cosmic ratio of baryons to
photons, a quantity inferred from observations of the microwave background. The
predicted primordial 7Li abundance is four times that measured in the
atmospheres of Galactic halo stars. This discrepancy could be caused by
modification of surface lithium abundances during the stars' lifetimes or by
physics beyond the Standard Model that affects early nucleosynthesis. The
lithium abundance of low-metallicity gas provides an alternative constraint on
the primordial abundance and cosmic evolution of lithium that is not
susceptible to the in situ modifications that may affect stellar atmospheres.
Here we report observations of interstellar 7Li in the low-metallicity gas of
the Small Magellanic Cloud, a nearby galaxy with a quarter the Sun's
metallicity. The present-day 7Li abundance of the Small Magellanic Cloud is
nearly equal to the BBN predictions, severely constraining the amount of
possible subsequent enrichment of the gas by stellar and cosmic-ray
nucleosynthesis. Our measurements can be reconciled with standard BBN with an
extremely fine-tuned depletion of stellar Li with metallicity. They are also
consistent with non-standard BBN.Comment: Published in Nature. Includes main text and Supplementary
Information. Replaced with final title and abstrac
Estimating the p-mode frequencies of the solar twin 18 Sco
Solar twins have been a focus of attention for more than a decade, because
their structure is extremely close to that of the Sun. Today, thanks to
high-precision spectrometers, it is possible to use asteroseismology to probe
their interiors. Our goal is to use time series obtained from the HARPS
spectrometer to extract the oscillation frequencies of 18 Sco, the brightest
solar twin. We used the tools of spectral analysis to estimate these
quantities. We estimate 52 frequencies using an MCMC algorithm. After
examination of their probability densities and comparison with results from
direct MAP optimization, we obtain a minimal set of 21 reliable modes. The
identification of each pulsation mode is straightforwardly accomplished by
comparing to the well-established solar pulsation modes. We also derived some
basic seismic indicators using these values. These results offer a good basis
to start a detailed seismic analysis of 18 Sco using stellar models.Comment: 12 pages, 6 figures, to be published in A&
Uncertainties in models of stellar structure and evolution
Numerous physical aspects of stellar physics have been presented in Ses- sion
2 and the underlying uncertainties have been tentatively assessed. We try here
to highlight some specific points raised after the talks and during the general
discus- sion at the end of the session and eventually at the end of the
workshop. A table of model uncertainties is then drawn with the help of the
participants in order to give the state of the art in stellar modeling
uncertainties as of July 2013.Comment: Proc. of the workshop "Asteroseismology of stellar populations in the
Milky Way" (Sesto, 22-26 July 2013), Astrophysics and Space Science
Proceedings, (eds. A. Miglio, L. Girardi, P. Eggenberger, J. Montalban
Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. II. Ages, metallicities, detailed elemental abundances, and connections to the Galactic thick disc
The Bulge is the least understood major stellar population of the Milky Way.
Most of what we know about the formation and evolution of the Bulge comes from
bright giant stars. The underlying assumption that giants represent all the
stars, and accurately trace the chemical evolution of a stellar population, is
under debate. In particular, recent observations of a few microlensed dwarf
stars give a very different picture of the evolution of the Bulge from that
given by the giant stars. [ABRIDGED] We perform a detailed elemental abundance
analysis of dwarf stars in the Galactic bulge, based on high-resolution spectra
that were obtained while the stars were optically magnified during
gravitational microlensing events. [ABRIDGED] We present detailed elemental
abundances and stellar ages for six new dwarf stars in the Galactic bulge.
Combining these with previous events, here re-analysed with the same methods,
we study a homogeneous sample of 15 stars, which constitute the largest sample
to date of microlensed dwarf stars in the Galactic bulge. We find that the
stars span the full range of metallicities from [Fe/H]=-0.72 to +0.54, and an
average metallicity of =-0.08+/-0.47, close to the average metallicity
based on giant stars in the Bulge. Furthermore, the stars follow well-defined
abundance trends, that for [Fe/H]<0 are very similar to those of the local
Galactic thick disc. This suggests that the Bulge and the thick disc have had,
at least partially, comparable chemical histories. At sub-solar metallicities
we find the Bulge dwarf stars to have consistently old ages, while at
super-solar metallicities we find a wide range of ages. Using the new age and
abundance results from the microlensed dwarf stars we investigate possible
formation scenarios for the Bulge.Comment: New version accepted for publication in Astronomy and Astrophysic
Heterogeneous subsidence and paleogeographic elements in an extensional setting revealed through the correlation of a storm deposit unit (Aptian, E Spain)
Durante el Aptiense, en la Subcuenca de Las Parras (NW Cuenca del Maestrazgo) se depositó una unidad siliciclástica en un contexto tectónico extensional. Esta unidad se ha dividido en cuatro secuencias granocrecientes, de las cuales se analiza en detalle la tercera (S3) ya que presenta un alto potencial de correlación lateral. El análisis sedimentológico de la secuencia S3 ha permitido interpretar una evolución vertical de shoreface inferior con procesos de tormenta, a shoreface superior; también ha permitido correlacionar esta secuencia entre dos sectores de la subcuenca que presentan un desarrollo litológico considerablemente diferente. El techo de la secuencia S3 es una superfi cie erosiva menor con valor cronoestratigráfi co y se ha utilizado como datum de correlación para el análisis de la unidad siliciclástica. Las variaciones laterales de facies de la secuencia S3 permiten interpretar la proximidad de un sistema de descarga siliciclástico hacia el sureste, y se propone una zona de intersección de fallas normales, próxima al sector suroriental de la zona estudiada, como un elemento paleoestructural favorable para la entrada de un sistema de drenaje en la cuenca. En el sector suroriental, por encima del datum de correlación, la secuencia S4 presenta un desarrollo muy reducido debido a la ausencia de su parte inferior; esto ha permitido interpretar la presencia de una discontinuidad local intra-S4. Esta discontinuidad local se correlaciona con otra reconocida en el sector noroccidental. Debido a las diferencias de espesor y al grado de desarrollo de la discontinuidad intra-S4 se deduce que la historia de subsidencia de diferentes bloques de la cuenca no es exactamente la misma. Esta discontinuidad intra-S4 podría tener interés regional ya que separa sedimentos dominantemente siliciclásticos de sedimentos carbonatados y podría indicar una modifi cación importante del sistema sedimentario. Para uno de los bloques estudiados, las variaciones espaciales de espesor para cada secuencia podrían representar un desarrollo de la subsidencia alternando periodos con subsidencia diferencial atenuada y periodos con subsidencia diferencial acentuada, que pueden estar relacionados con la dinámica extensional
Wind from the black-hole accretion disk driving a molecular outflow in an active galaxy
Powerful winds driven by active galactic nuclei (AGN) are often invoked to
play a fundamental role in the evolution of both supermassive black holes
(SMBHs) and their host galaxies, quenching star formation and explaining the
tight SMBH-galaxy relations. Recent observations of large-scale molecular
outflows in ultra-luminous infrared galaxies (ULIRGs) have provided the
evidence to support these studies, as they directly trace the gas out of which
stars form. Theoretical models suggest an origin of these outflows as
energy-conserving flows driven by fast AGN accretion disk winds. Previous
claims of a connection between large-scale molecular outflows and AGN activity
in ULIRGs were incomplete because they were lacking the detection of the
putative inner wind. Conversely, studies of powerful AGN accretion disk winds
to date have focused only on X-ray observations of local Seyferts and a few
higher redshift quasars. Here we show the clear detection of a powerful AGN
accretion disk wind with a mildly relativistic velocity of 0.25c in the X-ray
spectrum of IRAS F11119+3257, a nearby (z = 0.189) optically classified type 1
ULIRG hosting a powerful molecular outflow. The AGN is responsible for ~80% of
the emission, with a quasar-like luminosity of L_AGN = 1.5x10^46 erg/s. The
energetics of these winds are consistent with the energy-conserving mechanism,
which is the basis of the quasar mode feedback in AGN lacking powerful radio
jets.Comment: Revised file including the letter, methods and supplementary
information. Published in the March 26th 2015 issue of Natur
Observations of Outflowing UV Absorbers in NGC 4051 with the Cosmic Origins Spectrograph
We present new Hubble Space Telescope (HST)/Cosmic Origins Spectrograph
observations of the Narrow-Line Seyfert 1 galaxy NGC 4051. These data were
obtained as part of a coordinated observing program including X-ray
observations with the Chandra/High Energy Transmission Grating (HETG)
Spectrometer and Suzaku. We detected nine kinematic components of UV
absorption, which were previously identified using the HST/Space Telescope
Imaging Spectrograph. None of the absorption components showed evidence for
changes in column density or profile within the \sim 10 yr between the STIS and
COS observations, which we interpret as evidence of 1) saturation, for the
stronger components, or 2) very low densities, i.e., n_H < 1 cm^-3, for the
weaker components. After applying a +200 km s^-1 offset to the HETG spectrum,
we found that the radial velocities of the UV absorbers lay within the O VII
profile. Based on photoionization models, we suggest that, while UV components
2, 5 and 7 produce significant O VII absorption, the bulk of the X-ray
absorption detected in the HETG analysis occurs in more highly ionized gas.
Moreover, the mass loss rate is dominated by high ionization gas which lacks a
significant UV footprint.Comment: 41 pages, 10 Figures; accepted for publication in the Astrophysical
Journa
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