316 research outputs found
Petrogenetic aspects of Los Pedroches granodiorite (Central zone of Los Pedroches batholith, Córdoba, Spain)
[Resumen] Se ha realizado un estudio petrológico y geoquímico detallado de la granodiorita de Los Pedroches y de sus enclaves microgranitoides (sensu VERNON, 1983). Tanto en granodiorita como en enclaves se han obtenido datos de elementos mayores y trazas en roca total (incluidos REE) y datos de microsonda electrónica para las fases minerales mayoritarias. Se concluye que tanto las rocas estudiadas como sus enclaves pueden haber sido generados a partir de fundido(s) procedente(s) de un mismo protolito cortical, puesto que los datos geoquímicos de los enclaves no permiten inferir una hibridación de material cortical con cantidades significativas de material exótico. Se sugiere una explicación alternativa para la generación de los enclaves microgranitoides estudiados, que permite explicar tanto su naturaleza ígnea como la totalidad de sp::; rasgos geoquímicos[Abstract] A detailed petrologic and geochemical study of Los Pedroches granodiorite and its microgranitoid enclaves (sensu VERNON, 1983) has been performed. Wholerock major and trace elements (including REE) chemical data and electron microprobe mineral analysis of mayor phases have been obtained, both from granodiorites and microgranitoid enclaves. It is concluded that both studied rocks and their enclaves can have been generated from melt(s) derived from the same crustal protolith, since geochemical data from enclaves do not permit to deduce an hybridization of crustal melts with signifcants amounts of exotic material. An alternative explanation of studied microgranitoid enclaves, allowing to interprete both their igneous character and aH their observed geochemical features is suggested
Topological Defects from First Order Gauge Theory Phase Transitions
We investigate the mechanism by which topological defects form in first order
phase transitions with a charged order parameter. We show how thick
superconductor vortices and heavy cosmic strings form by trapping of magnetic
flux. In an external magnetic field, intermediate objects such as strips and
membranes of magnetic flux and chains of single winding defects are produced.
At non-zero temperature, a variety of spontaneous defects of different winding
numbers arise. In cosmology, our results mean that the magnetic flux thermal
fluctuations get trapped in a primordial multi-tension string network. The
mechanism may also apply to the production of cosmic-like strings in brane
collisions. In a thin type-I superconductor film, flux strips are found to be
meta-stable while thick vortices are stable up to some critical value of the
winding number which increases with the thickness of the film. In addition, a
non-dissipative Josephson-like current is obtained across the strips of
quantized magnetic flux.Comment: Corrections made on sections 4,5. Higher quality figures in published
versio
Herschel observations of the circumstellar environment of the two Herbig Be stars R Mon and PDS27
We report and analyse FIR observations of two Herbig Be stars, R Mon and PDS
27, obtained with Herschel's instruments PACS and SPIRE. We construct SEDs and
derive the infrared excess. We extract line fluxes from the PACS and SPIRE
spectra and construct rotational diagrams in order to estimate the excitation
temperature of the gas. We derive CO, [OI] and [CI] luminosities to determine
physical conditions of the gas, as well as the dominant cooling mechanism. We
confirm that the Herbig Be stars are surrounded by remnants from their parental
clouds, with an IR excess that mainly originates in a disc. In R Mon we detect
[OI], [CI], [CII], CO (26 transitions), water and OH, while in PDS 27 we only
detect [CI] and CO (8 transitions). We attribute the absence of OH and water in
PDS 27 to UV photo-dissociation and photo-evaporation. From the rotational
diagrams, we find several components for CO: we derive 94990 K,
35820 K & 7712 K for R Mon, 9612 K & 314 K for PDS 27 and
258 K & 276 K for their respective compact neighbours. The forsterite
feature at 69m was not detected in either of the sources, probably due to
the lack of (warm) crystalline dust in a flat disc. We find that cooling by
molecules is dominant in the Herbig Be stars, while this is not the case in
Herbig Ae stars where cooling by [OI] dominates. Moreover, we show that in the
Herbig Be star R Mon, outflow shocks are the dominant gas heating mechanism,
while in Herbig Ae stars this is stellar. The outflow of R Mon contributes to
the observed line emission by heating the gas, both in the central spaxel/beam
covering the disc and the immediate surroundings, as well as in those
spaxels/beams covering the parabolic shell around it. PDS 27, a B2 star, has
dispersed a large part of its gas content and/or destroyed molecules; this is
likely given its intense UV field.Comment: Accepted for publication in Astronomy & Astrophysic
Fluxoid formation: size effects and non-equilibrium universality
Simple causal arguments put forward by Kibble and Zurek suggest that the
scaling behaviour of condensed matter at continuous transitions is related to
the familiar universality classes of the systems at quasi-equilibrium. Although
proposed 25 years ago or more, it is only in the last few years that it has
been possible to devise experiments from which scaling exponents can be
determined and in which this scenario can be tested. In previous work, an
unusually high Kibble-Zurek scaling exponent was reported for spontaneous
fluxoid production in a single isolated superconducting Nb loop, albeit with
low density. Using analytic approximations backed up by Langevin simulations,
we argue that densities as small as these are too low to be attributable to
scaling, and are conditioned by the small size of the loop. We also reflect on
the physical differences between slow quenches and small rings, and derive some
criteria for these differences, noting that recent work on slow quenches does
not adequately explain the anomalous behaviour seen here.Comment: 7 pages, 4 figures, presentation given at CMMP 201
Defect formation in superconducting rings: external fields and finite-size effects
Consistent with the predictions of Kibble and Zurek, scaling behaviour has
been seen in the production of fluxoids during temperature quenches of
superconducting rings. However, deviations from the canonical behaviour arise
because of finite-size effects and stray external fields.
Technical developments, including laser heating and the use of long Josephson
tunnel junctions, have improved the quality of data that can be obtained. With
new experiments in mind we perform large-scale 3D simulations of quenches of
small, thin rings of various geometries with fully dynamical electromagnetic
fields, at nonzero externally applied magnetic flux. We find that the outcomes
are, in practice, indistinguishable from those of much simpler Gaussian
analytical approximations in which the rings are treated as one-dimensional
systems and the magnetic field fluctuation-free.Comment: 10 pages, 3 figures, presentation at QFS2012, to appear in JLT
Multiwavelength characterisation of an ACT-selected, lensed dusty star-forming galaxy at z=2.64
We present \ci\,(2--1) and multi-transition CO observations of a dusty
star-forming galaxy, ACT\,J2029+0120, which we spectroscopically confirm to lie
at \,=\,2.64. We detect CO(3--2), CO(5--4), CO(7--6), CO(8--7), and
\ci\,(2--1) at high significance, tentatively detect HCO(4--3), and place
strong upper limits on the integrated strength of dense gas tracers (HCN(4--3)
and CS(7--6)). Multi-transition CO observations and dense gas tracers can
provide valuable constraints on the molecular gas content and excitation
conditions in high-redshift galaxies. We therefore use this unique data set to
construct a CO spectral line energy distribution (SLED) of the source, which is
most consistent with that of a ULIRG/Seyfert or QSO host object in the taxonomy
of the \textit{Herschel} Comprehensive ULIRG Emission Survey. We employ RADEX
models to fit the peak of the CO SLED, inferring a temperature of T117 K
and cm, most consistent with a ULIRG/QSO object
and the presence of high density tracers. We also find that the velocity width
of the \ci\ line is potentially larger than seen in all CO transitions for this
object, and that the ratio is also larger
than seen in other lensed and unlensed submillimeter galaxies and QSO hosts; if
confirmed, this anomaly could be an effect of differential lensing of a shocked
molecular outflow.Comment: Accepted for publication in Ap
Spectral Stacking of Radio-Interferometric Data
Mapping molecular line emission beyond the bright low-J CO transitions is
still challenging in extragalactic studies, even with the latest generation of
(sub-)mm interferometers, such as ALMA and NOEMA. We summarise and test a
spectral stacking method that has been used in the literature to recover
low-intensity molecular line emission, such as HCN(1-0), HCO+(1-0), and even
fainter lines in external galaxies. The goal is to study the capabilities and
limitations of the stacking technique when applied to imaged interferometric
observations. The core idea of spectral stacking is to align spectra of the low
S/N spectral lines to a known velocity field calculated from a higher S/N line
expected to share the kinematics of the fainter line, e.g., CO(1-0) or 21-cm
emission. Then these aligned spectra can be coherently averaged to produce
potentially high S/N spectral stacks. Here, we use imaged simulated
interferometric and total power observations at different signal-to-noise
levels, based on real CO observations. For the combined interferometric and
total power data, we find that the spectral stacking technique is capable of
recovering the integrated intensities even at low S/N levels across most of the
region where the high S/N prior is detected. However, when stacking
interferometer-only data for low S/N emission, the stacks can miss up to 50% of
the emission from the fainter line. A key result of this analysis is that the
spectral stacking method is able to recover the true mean line intensities in
low S/N cubes and to accurately measure the statistical significance of the
recovered lines. To facilitate the application of this technique we provide a
public Python package, called PyStacker.Comment: 10 pages, 10 figures, accepted for pub in A&A, Apr 28, 202
Resolved low-J CO excitation at 190 parsec resolution across NGC 2903 and NGC 3627
The low- rotational transitions of CO are commonly used to trace
the distribution of molecular gas in galaxies. Their ratios are sensitive to
excitation and physical conditions in the molecular gas. Spatially resolved
studies of CO ratios are still sparse and affected by flux calibration
uncertainties, especially since most do not have high angular resolution or do
not have short-spacing information and hence miss any diffuse emission. We
compare the low- CO ratios across the disk of two massive, star-forming
spiral galaxies NGC2903 and NGC3627 to investigate whether and how local
environments drive excitation variations at GMC scales. We use Atacama Large
Millimeter Array (ALMA) observations of the three lowest- CO transitions at
a common angular resolution of 4 (190pc). We measure median line ratios of
, , and
across the full disk of NGC3627. We see clear CO
line ratio variation across the galaxy consistent with changes in temperature
and density of the molecular gas. In particular, toward the center, ,
, and increase by 35\%, 50\%, and 66\%, respectively compared
to their average disk values. The overall line ratio trends suggest that
CO(3-2) is more sensitive to changes in the excitation conditions than the two
lower- transitions. Furthermore, we find a similar radial trend in
NGC2903, albite a larger disk-wide average of . We conclude that the CO low- line
ratios vary across environments in such a way that they can trace changes in
the molecular gas conditions, with the main driver being changes in
temperature.Comment: accepted for publication in MNRAS, 17 pages, 16 figure
- …