362 research outputs found
Herschel/HIFI observations of molecular emission in protoplanetary nebulae and young planetary nebulae
We performed Herschel/HIFI observations of intermediate-excitation molecular
lines in the far-infrared/submillimeter range in a sample of ten protoplanetary
nebulae and young planetary nebulae. The high spectral resolution provided by
HIFI yields accurate measurements of the line profiles. The observation of
these high-energy transitions allows an accurate study of the excitation
conditions, particularly in the warm gas, which cannot be properly studied from
the low-energy lines.
We have detected FIR/sub-mm lines of several molecules, in particular of
12CO, 13CO, and H2O. Emission from other species, like NH3, OH, H2^{18}O, HCN,
SiO, etc, has been also detected. Wide profiles showing sometimes spectacular
line wings have been found. We have mainly studied the excitation properties of
the high-velocity emission, which is known to come from fast bipolar outflows.
From comparison with general theoretical predictions, we find that CRL 618
shows a particularly warm fast wind, with characteristic kinetic temperature Tk
>~ 200 K. In contrast, the fast winds in OH 231.8+4.2 and NGC 6302 are cold, Tk
~ 30 K. Other nebulae, like CRL 2688, show intermediate temperatures, with
characteristic values around 100 K. We also discuss how the complex structure
of the nebulae can affect our estimates, considering two-component models. We
argue that the differences in temperature in the different nebulae can be due
to cooling after the gas acceleration (that is probably due to shocks); for
instance, CRL 618 is a case of very recent acceleration, less than ~ 100 yr
ago, while the fast gas in OH 231.8+4.2 was accelerated ~ 1000 yr ago. We also
find indications that the densest gas tends to be cooler, which may be
explained by the expected increase of the radiative cooling efficiency with the
density.Comment: 24 pages, 31 figure
A contribution to the quantification of crustal shortening and kinematics of deformation across the Western Andes ( ∼ 20–22° S)
The Andes are an emblematic active Cordilleran orogen.
Mountain building in the Central Andes (∼20∘ S)
started by the Late Cretaceous to early Cenozoic along the subduction margin
and propagated eastward. In general, the structures sustaining the uplift of
the western flank of the Andes are dismissed, and their contribution to
mountain building remains poorly constrained. Here, we focus on two sites
along the Western Andes at ∼20–22∘ S in the
Atacama desert, where structures are well exposed. We combine mapping from
high-resolution satellite images with field observations and numerical
trishear forward modeling to provide quantitative constraints on the
kinematic evolution of the investigated field sites. When upscaling our
local field interpretations to the regional scale, we identify two main
structures: (1) the Andean Basement Thrust, a west-vergent thrust system
placing Andean Paleozoic basement over Mesozoic strata, and (2) a series of
west-vergent thrusts pertaining to the West Andean Thrust System, deforming
primarily Mesozoic units. From our interpreted sections, we estimate that
both structures together accommodate at least ∼6–9 km of
shortening across the sole investigated ∼7–17 km wide field
sites. This multi-kilometric shortening represents only a fraction of the
total shortening accommodated across the whole Western Andes. The timing of
the main deformation recorded in the folded Mesozoic series can be bracketed
between ∼68 and ∼29 Ma – and possibly between
∼68 and ∼44 Ma – from dated deformed
geological layers, with a subsequent significant slowing-down of shortening
rates. Even though the structures forming the Western Andes only absorbed a
small fraction of the total shortening across the whole orogen, their
contribution was relatively significant at the earliest stages of
Andean mountain building before deformation proceeded eastward.</p
Discriminating sources and preservation of organic matter in surface sediments from five Antarctic lakes in the Fildes Peninsula (King George Island) by lipid biomarkers and compound-specific isotopic analysis
Lakes are important paleoenvironmental archives retaining abundant information due to their typical high sedimentation rates and susceptibility to environmental changes. Here, we scrutinize the organic matter (OM) composition, origin and preservation state in surface sediments from five lakes in a remote, warming-sensitive, and poorly explored region partially covered by the retreating Collins Glacier in King George Island (Antarctica), the Fildes Peninsula. Lipid biomarkers of terrestrial origin (i.e. high-molecularweight n-alkanes, n-alkanoic acids, and n-alkanols; β-sitosterol, campesterol, and stigmasterol) were detected in the five Fildes Lakes, with the smallest basin (i.e.,Meltwater) showing a particularly strongmoss imprint. Aquatic source indicators such as lowC/N and terrestrial over aquatic ratios (TAR), or less negative δ13C valueswere preferentially found in themid-sized lakes (i.e., Drake and Ionospheric). Sedimentary carbon in the larger lakes (i.e., Uruguay and Kitezh) displayed a largely biogenic origin (i.e., values of carbon preference index, CPI, ≫1), whereas the three lakes close to Collins Glacier (i.e., Drake, Meltwater, and Ionospheric) showed certain contribution from petrogenic sources (CPI ~ 1). The results suggest that the geochemical signature of the surface sediments in the five Fildes lakes is determined by factors such as the distance to the retreating Collins Glacier, the proximity to the coast, or the lake depth. This study illustrates the forensic interest of combining lipid biomarkers, compound-specific isotopic analysis, and bulk geochemistry to reconstruct paleoenvironments and study climate-sensitive regions
Optimal Control of Molecular Spin Qudits
We demonstrate, numerically, the possibility of manipulating the spin states of molecular nanomagnets with shaped microwave pulses designed with quantum optimal control theory techniques. The state-to-state or full gate transformations can be performed in this way in shorter times than using simple monochromatic resonant pulses. This enhancement in the operation rates can therefore mitigate the effect of decoherence. The optimization protocols and their potential for practical implementations are illustrated by simulations performed for a simple molecular cluster hosting a single Gd3+ ion. Its eight accessible levels (corresponding to a total spin S=7/2) allow encoding an eight-level qudit or a system of three coupled qubits. All necessary gates required for universal operation can be obtained with optimal pulses using the intrinsic couplings present in this system. The application of optimal control techniques can facilitate the implementation of quantum technologies based on molecular spin qudits
New observations and models of circumstellar CO line emission of AGB stars in the Herschel SUCCESS programme
CONTEXT: Asymptotic giant branch (AGB) stars are in one of the latest
evolutionary stages of low to intermediate-mass stars. Their vigorous mass loss
has a significant effect on the stellar evolution, and is a significant source
of heavy elements and dust grains for the interstellar medium. The mass-loss
rate can be well traced by carbon monoxide (CO) line emission.
AIMS: We present new Herschel HIFI and IRAM 30m telescope CO line data for a
sample of 53 galactic AGB stars. The lines cover a fairly large range of
excitation energy from the line to the line, and even the
line in a few cases. We perform radiative transfer modelling for 38
of these sources to estimate their mass-loss rates.
METHODS: We used a radiative transfer code based on the Monte Carlo method to
model the CO line emission. We assume spherically symmetric circumstellar
envelopes that are formed by a constant mass-loss rate through a smoothly
accelerating wind.
RESULTS: We find models that are consistent across a broad range of CO lines
for most of the stars in our sample, i.e., a large number of the circumstellar
envelopes can be described with a constant mass-loss rate. We also find that an
accelerating wind is required to fit, in particular, the higher-J lines and
that a velocity law will have a significant effect on the model line
intensities. The results cover a wide range of mass-loss rates (
to ) and gas expansion
velocities (2 to km s), and include M-, S-, and C-type AGB stars.
Our results generally agree with those of earlier studies, although we tend to
find slightly lower mass-loss rates by about 40%, on average. We also present
"bonus" lines detected during our CO observations.Comment: 36 page
Methanogenesis at high temperature, high ionic strength and low pH in the volcanic area of Dallol, Ethiopia
The Dallol geothermal area originated as a result of seismic activity and the presence of a shallow underground volcano, both due to the divergence of two tectonic plates. In its ascent, hot water dissolves and drags away the subsurface salts. The temperature of the water that comes out of the chimneys is higher than 100C, with a pH close to zero and high mineral concentration. These factors make Dallol a polyextreme environment. So far, nanohaloarchaeas, present in the salts that form the walls of the chimneys, have been the only living beings reported in this extreme environment. Through the use of complementary techniques: culture in microcosms, methane stable isotope signature and hybridization with specific probes, the methanogenic activity in the Dallol area has been assessed. Methane production in microcosms, positive hybridization with the Methanosarcinales probe and the δC-values measured, show the existence of extensive methanogenic activity in the hydrogeothermic Dallol system. A methylotrophic pathway, carried out by Methanohalobium and Methanosarcina-like genera, could be the dominant pathway for methane production in this environment.Agencia Estatal de Investigación (AEI), grant MDM-2017-0737 (Unidad de Excelencia “María de Maeztu”-Centro de Astrobiología INTA-CSIC) and the Spanish Ministerio de Ciencia e Innovación (MICINN
Massive expanding torus and fast outflow in planetary nebula NGC 6302
We present interferometric observations of CO and CO =21
emission from the butterfly-shaped, young planetary nebula NGC 6302. The high
angular resolution and high sensitivity achieved in our observations allow us
to resolve the nebula into two distinct kinematic components: (1) a massive
expanding torus seen almost edge-on and oriented in the North-South direction,
roughly perpendicular to the optical nebula axis. The torus exhibits very
complex and fragmentated structure; (2) high velocity molecular knots moving at
high velocity, higher than 20 \kms, and located in the optical bipolar lobes.
These knots show a linear position-velocity gradient (Hubble-like flow), which
is characteristic of fast molecular outflow in young planetary nebulae. From
the low but variable CO/CO =21 line intensity ratio we
conclude that the CO =21 emission is optically thick over much of
the nebula. Using the optically thinner line CO =21 we estimate a
total molecular gas mass of 0.1 M, comparable to the ionized gas
mass; the total gas mass of the NGC 6302 nebula, including the massive ionized
gas from photon dominated region, is found to be 0.5 M. From
radiative transfer modelling we infer that the torus is seen at inclination
angle of 75 with respect to the plane of the sky and expanding at
velocity of 15 \kms. Comparison with recent observations of molecular gas in
NGC 6302 is also discussed.Comment: 24 pages, 7 figures, accepted for publication in Astrophysical
Journa
Zooming on the emerging ionized regions of pPNe with ALMA
We report on recent results from our successful and pioneering observational
program with ALMA to study emerging ultracom pact HII regions of pre-Planetary
Nebulae (pPNe) using mm-wavelength recombination lines (mRRLs) as new optimal
tracers. We focus on our study of two poster-child pPNe, namely, M2-9 and
CRL618. We reveal the structure and kinematics of the en igmatic inner nebular
regions of these objects with an unprecedented angular resolution down to
20-30mas (~15-30AU). For both targets, the ionized central regions are
elongated along the main symmetry axis of the large-scale nebulae, consiste nt
with bipolar winds, and show notable axial velocity gradients with expansion
velocities of up to ~100km/s. The H30a pr ofiles exhibit time variability,
reflecting changes in the physical properties and kinematics on scales of a few
years. O ur ongoing analysis employs 3D, non-LTE radiative transfer modeling,
providing a detailed description of the innermost la yers of these well known
pPNe with exceptional clarity.Comment: 6 pages, 3 figures. Proceedings IAU Symposium no. 38
Low-excitation atomic gas around evolved stars: II. ISO observations of O-rich nebulae
We have observed atomic fine-structure lines in the far-infrared (FIR) from 12 oxygen-rich evolved stars. The sample is composed of mostly proto-planetary nebulae (PPNe) and some planetary nebulae (PNe) and asymptotic giant branch (AGB) stars. ISO LWS and SWS observations of [O I], [C II], [N II], [Si I], [Si II], [S I], [Fe I], and [Fe II] lines were obtained. Taking into account also the sample presented by Fong et al. (Paper I) of carbon-rich evolved stars, we find that PPNe emit in these low-excitation atomic transitions only when the central star is hotter than ∼10 000 K. This result suggests that such lines predominantly arise from photodissociation regions (PDRs), and not from shocked regions. The line widths determined from our Fabry-Perot data also suggest that the FIR lines arise from relatively quiescent PDR gas, as opposed to shocked gas. Our results are in reasonable agreement with predictions from PDR emission models, allowing the estimation of the density of the emitting layers by comparison with the model results. On the other hand, the comparison with predictions of the emission from J-type and C-type shocked regions suggests that detected lines do not come from shocks. The [C II] line flux has been used to measure the mass of the low-excitation atomic component in PPNe, since this transition has been found to be a useful model-independent probe to estimate the total mass of these PDRs. The derivation of the mass formula and assumptions made are also discussed
Meconio y exposición prenatal a neurotóxicos
6 pages, 1 figures, 2 tables.[ESP] Introducción. La ubicuidad con la que se encuentran la mayoría de las substancias neurotóxicas en el medio ambiente implica a los pediatras en la necesidad de desarrollar
métodos para medir la magnitud de la exposición durante los periodos vulnerables del desarrollo. Una forma útil de abordar este problema consiste en analizar muestras biológicas que acumulen las substancias neurotóxicas o sus metabolitos durante el periodo fetal.Método. Revisión bibliográfica sistemática de los últimos 20 años obtenida principalmente de Medline; Science Citation Index y Embase sobre los estudios con meconio como matriz de exposición prenatal a substancias neurotóxicas. El perfil de búsqueda utilizado fue: meconium, prenatal
exposure, biological markers, matrices, environmental pollutants, nervous system poisonings, neurotoxicity sindromes.
Hemos seleccionado los trabajos más importantes y de sus referencias se han obtenido los más relevantes de los años previos a la búsqueda.Resultados. Tradicionalmente, los esfuerzos para determinar la exposición fetal se han centrado en el análisis de sangre de cordón u orina de la madre o el neonato. El meconio
es fácilmente disponible, es inerte, acumula los neurotóxicos y/o sus metabolitos desde la semana 12 de gestación donde quedan “fosilizados” hasta el nacimiento. Puede constituir un instrumento muy importante para investigar la exposición fetal a los distintos contaminantes ambientales y en particular a neurotóxicos.Conclusiones.
Las exposiciones fetales a los distintos neurotóxicos estudiados a través de sangre materna, de cordón, pelo, uña, placenta y orina parecen ser menos predictivas sobre los efectos neurológicos que las mediciones de los mismos realizadas en meconio. Son necesarios más estudios en este campo.Implementar y desarrollar la medida en meconio de una amplia gama de sustancias neurotóxicas ayudará en la práctica pediátrica a una intervención e identificación temprana mostrando las exposiciones que puedan provocar daño y facilitando el desarrollo de medidas preventivas y rehabilitadoras.[ENG] Brackground. The environmental ubiquity of most neurotoxicants implies the pediatricians in the development of methods for exposure measurement during the vulnerable periods of development. The analysis of biological samples able to accumulate the neurotoxicant substances or its metabolites during the fetal period is a useful approach to fulfil this objective.Material and methods. A systematic literature review of the last 20 years in Medline, Science Citation Index and Embase
on the studies with meconium like womb of prenatal exposure to neurotoxicants has been undertaken. The search profile was: “meconium”, “prenatal exposure”, “biological
markers”, “matrices”, “environmental pollutants”, “nervous system poisonings”, “neurotoxicity sindromes”. We selected the most relevant articles and retrieved more
from their references.Results. Traditionally, the efforts to determine the fetal exposure have been centered in the analysis of cord blood,
urinates of the mother or of the neonato. Meconium is easily available, inert, accumulates the neurotoxicants and/or
its metabolitos from week 12 of gestation where they are "fossilized" until the birth. It can constitute a very important
instrument for the investigation of the fetal exposure to the different environmental pollutants and in particular
to neurotoxicants.Conclusions.
Foetal exposure to different neurotoxicants monitored from maternal blood, cord blood, hair, fingernail, placenta and urinates seem to be less predictive for neurological
effects than meconium. However, more studies are needed to confirm this hypothesis.Implementation and measurement in meconium of a wide range of neurotoxic substances will be of help in the pediatric practice for intervention and early identification
as it will reveal harmful exposures and facilitate the implementation of preventive measures.Los autores quieren expresar su agradecimiento a los miembros de la red de Investigación Colaborativa INMA, y en especial a Amparo Quiles Latorre, Elena Romero Aliaga y Sandra Pérez Aliaga, por su apoyo y colaboración en la realización del trabajo de campo; al equipo de enfermería
de la 7ª, 8ª y 9ª de la maternidad del Hospital Materno-Infantil Universitario La Fe y a los recién nacidos y sus felices
padres que con su colaboración y entusiasmo hacen posible llevar a término estos estudios.Peer reviewe
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