112 research outputs found
Estimation of the XUV radiation onto close planets and their evaporation
Context: The current distribution of planet mass vs. incident stellar X-ray
flux supports the idea that photoevaporation of the atmosphere may take place
in close-in planets. Integrated effects have to be accounted for. A proper
calculation of the mass loss rate due to photoevaporation requires to estimate
the total irradiation from the whole XUV range. Aims: The purpose of this paper
is to extend the analysis of the photoevaporation in planetary atmospheres from
the accessible X-rays to the mostly unobserved EUV range by using the coronal
models of stars to calculate the EUV contribution to the stellar spectra. The
mass evolution of planets can be traced assuming that thermal losses dominate
the mass loss of their atmospheres. Methods: We determine coronal models for 82
stars with exoplanets that have X-ray observations available. Then a synthetic
spectrum is produced for the whole XUV range (~1-912 {\AA}). The determination
of the EUV stellar flux, calibrated with real EUV data, allows us to calculate
the accumulated effects of the XUV irradiation on the planet atmosphere with
time, as well as the mass evolution for planets with known density. Results: We
calibrate for the first time a relation of the EUV luminosity with stellar age
valid for late-type stars. In a sample of 109 exoplanets, few planets with
masses larger than ~1.5 Mj receive high XUV flux, suggesting that intense
photoevaporation takes place in a short period of time, as previously found in
X-rays. The scenario is also consistent with the observed distribution of
planet masses with density. The accumulated effects of photoevaporation over
time indicate that HD 209458b may have lost 0.2 Mj since an age of 20 Myr.
Conclusions: Coronal radiation produces rapid photoevaporation of the
atmospheres of planets close to young late-type stars. More complex models are
needed to explain fully the observations.Comment: Accepted by A&A. 10 pages, 8 figures, 7 Tables (2 online). Additional
online material includes 7 pages, 6 figures and 6 tables, all include
A scenario of planet erosion by coronal radiation
Context: According to theory, high-energy emission from the coronae of cool
stars can severely erode the atmospheres of orbiting planets. No observational
tests of the long term effects of erosion have yet been made. Aims: To analyze
the current distribution of planetary mass with X-ray irradiation of the
atmospheres in order to make an observational assessment of the effects of
erosion by coronal radiation. Methods: We study a large sample of
planet-hosting stars with XMM-Newton, Chandra and ROSAT; make a careful
identification of X-ray counterparts; and fit their spectra to make accurately
measurements of the stellar X-ray flux. Results: The distribution of the
planetary masses with X-ray flux suggests that erosion has taken place: most
surviving massive planets, (M_p sin i >1.5 M_J), have been exposed to lower
accumulated irradiation. Heavy erosion during the initial stages of stellar
evolution is followed by a phase of much weaker erosion. A line dividing these
two phases could be present, showing a strong dependence on planet mass.
Although a larger sample will be required to establish a well-defined erosion
line, the distribution found is very suggestive. Conclusions: The distribution
of planetary mass with X-ray flux is consistent with a scenario in which planet
atmospheres have suffered the effects of erosion by coronal X-ray and EUV
emission. The erosion line is an observational constraint to models of
atmospheric erosion.Comment: A&A 511, L8 (2010). 4 pages, 3 figures, 1 online table (included).
Language edited; corrected a wrong unit conversion (g/s -> M_J/Gyr);
corrected values in column 12 of Table 1 (slightly underestimated in first
version), and Figure 2 updated accordingl
Enclavijado de Ender en las fracturas del macizo trocantéreo: análisis retrospectivo de la ocupación del canal medular
Se revisaron las historias clínicas de 226 pacientes afectos de fracturas del macizo
trocantérico, tratadas mediante enclavijado de Ender en un periodo de 9 años en el Hospital
del Insalud de Barbastro. La estabilidad de las fracturas se determinó mediante la
clasificación de Ramadier. Se valoró el porcentaje de ocupación de la cavidad medular femoral por los clavos de Ender y la posible relación de este parámetro con la migración del material de osteosíntesis. Se evaluó también la utilidad del bloqueo distal de los clavos de Ender con agujas de Kirschner, en la prevención de su migración distal. Se comprobó una relación significativa entre el porcentaje de ocupación del canal medular y la migración distal del material en las fracturas inestables. El bloqueo distal con aguja de Kirschner no se acompañó de una menor incidencia en la migración distal de los clavos.A retrospective study was done on 226 trochanteric fractures managed with
Ender nails during a 9 years period at the Insalud Hospital of Barbastro. Stability of these fractures was classified following Ramadier's criteria. Filling of the medular cavity by Ender nails and its relation with osteosyntehsis migration was analysed. Distal locking of Ender nails by Kirschner pins was evaluated to prevent its distal mobilization. A significative relationship was observed between a high filling rate of the medular cavity and lower distal migration rate in unestable trochanteric fractures. Distal locking of Ender nails was not accompanied of lower rate of distal osteosynthesis migratio
Repercusiones de los ritmos reproductivos en un rebaño extensivo de raza manchega de carne
Se muestra la evolución de los resultados productivos en los últimos 22 años de una explotación de ovino de carne de la raza Manchega, destinado a la producción de lechazo, en función del sistema de cubriciones aplicado, el número de machos en cubrición y la utilización de melatonina para las cubriciones en épocas de anestro. Desde 1985 a 1992 se aplicaba en la explotación un sistema de tres partos en dos años. En 1993 se comenzó a utilizar el sistema STAR, de 5 cubriciones al año. En 2000 se aumentó el número de machos a más de un 5%. A partir de 2002 se comenzó a aplicar melatonina en las cubriciones que establece el sistema STAR en anestro estacionario (marzo y junio). Todas las modificaciones han mostrado beneficios en los resultados productivos. Los resultados de los últimos 5 años muestran la eficacia y la compatibilidad del sistema STAR en nuestras explotaciones de ovino en extensivo, acompañado de un número de machos importante que asegure buenas cubriciones (>5%). La aplicación de la melatonina optimiza este sistema de manejo, estabilizando las cubriciones de anestro, lo que hace que se produzca un mayor número de corderos útiles (vendidos + reposición), una venta de corderos mayor en el segundo semestre y se estabilicen los resultados entre años
HST PanCET program: A Cloudy Atmosphere for the promising JWST target WASP-101b
We present results from the first observations of the Hubble Space Telescope
(HST) Panchromatic Comparative Exoplanet Treasury (PanCET) program for
WASP-101b, a highly inflated hot Jupiter and one of the community targets
proposed for the James Webb Space Telescope (JWST) Early Release Science (ERS)
program. From a single HST Wide Field Camera 3 (WFC3) observation, we find that
the near-infrared transmission spectrum of WASP-101b contains no significant
HO absorption features and we rule out a clear atmosphere at 13{\sigma}.
Therefore, WASP-101b is not an optimum target for a JWST ERS program aimed at
observing strong molecular transmission features. We compare WASP-101b to the
well studied and nearly identical hot Jupiter WASP-31b. These twin planets show
similar temperature-pressure profiles and atmospheric features in the
near-infrared. We suggest exoplanets in the same parameter space as WASP-101b
and WASP-31b will also exhibit cloudy transmission spectral features. For
future HST exoplanet studies, our analysis also suggests that a lower count
limit needs to be exceeded per pixel on the detector in order to avoid unwanted
instrumental systematics.Comment: 7 pages, 4 figures, 1 table, Accepted to ApJ
Impact of Oxygen Vacancy Occupancy on Charge Carrier Dynamics in BiVO4 Photoanodes
Oxygen vacancies are ubiquitous in metal oxides and critical to performance, yet the impact of these states upon charge carrier dynamics important for photoelectrochemical and photocatalytic applications remains contentious and poorly understood. A key challenge is the unambiguous identification of spectroscopic fingerprints which can be used to track their function. Herein, we employ five complementary techniques to modulate the electronic occupancy of states associated with oxygen vacancies in situ in BiVO4 photoanodes, allowing us to identify a spectral signature for the ionization of these states. We obtain an activation energy of ∼0.2 eV for this ionization process, with thermally activated electron detrapping from these states determining the kinetics of electron extraction, consistent with improved photoelectrochemical performance at higher temperatures. Bulk, un-ionized states, however, function as deep hole traps, with such trapped holes energetically unable to drive water oxidation. These observations help address recent controversies in the literature regarding oxygen vacancy function, providing new insights into their impact upon photoelectrochemical performance
A microscopic model for thin film spreading
A microscopic, driven lattice gas model is proposed for the dynamics and
spatio-temporal fluctuations of the precursor film observed in spreading
experiments. Matter is transported both by holes and particles, and the
distribution of each can be described by driven diffusion with a moving
boundary. This picture leads to a stochastic partial differential equation for
the shape of the boundary, which agrees with the simulations of the lattice
gas. Preliminary results for flow in a thermal gradient are discussed.Comment: 4 pages, 3 figures. Submitte
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Use of antibiotics and the prevalence of antibiotic-associated diarrhoea in patients with spinal cord injuries: an international, multi-centre study
BACKGROUND: Little is known about the use of antibiotics and the extent of antibiotic-associated diarrhoea (AAD) in patients with spinal cord injuries (SCIs).
AIMS: To record the use of antibiotics, establish the prevalence of AAD and Clostridium difficile infection (CDI), and assess if there was any seasonal variation in antibiotic use and incidence of AAD in patients with SCIs.
METHODS: A retrospective study was conducted in six European SCI centres between October 2014 and June 2015. AAD was defined as two or more watery stools (Bristol Stool Scale type 5, 6 or 7) over 24 h.
FINDINGS: In total, 1267 adults (median age 54 years, 30.7% female) with SCIs (52.7% tetraplegia, 59% complete SCI) were included in this study. Among the 215 (17%) patients on antibiotics, the top three indications for antibiotics were urinary tract infections (UTIs), infected pressure ulcers and other skin infections. Thirty-two of these 215 (14.9%) patients developed AAD and two patients out of the total study population (2/1267; 0.16%) developed CDI. AAD was more common in summer than in spring, autumn or winter (30.3% vs 3.8%, 7.4% and 16.9%, respectively; P<0.01). AAD was associated with age ≥65 years, tetraplegia, higher body mass index, hypoalbuminaemia, polypharmacy, multiple antibiotic use and high-risk antibiotic use. Summer and winter seasons and male sex were identified as independent predictors for the development of AAD.
CONCLUSION: This survey found that AAD is common in patients with SCIs, and UTI is the most common cause of infection. Summer and winter seasons and male sex are unique predictors for AAD. Both AAD and UTIs are potentially preventable; therefore, further work should focus on preventing the over-use of antibiotics, and developing strategies to improve hospital infection control measures
Temporal variations in the evaporating atmosphere of the exoplanet HD 189733b
Atmospheric escape has been detected from the exoplanet HD 209458b through
transit observations of the hydrogen Lyman-alpha line. Here we present
spectrally resolved Lyman-alpha transit observations of the exoplanet HD
189733b at two different epochs. These HST/STIS observations show for the first
time, that there are significant temporal variations in the physical conditions
of an evaporating planetary atmosphere. While atmospheric hydrogen is not
detected in the first epoch observations, it is observed at the second epoch,
producing a transit absorption depth of 14.4+/-3.6% between velocities of -230
to -140 km/s. Contrary to HD 209458b, these high velocities cannot arise from
radiation pressure alone and require an additional acceleration mechanism, such
as interactions with stellar wind protons. The observed absorption can be
explained by an atmospheric escape rate of neutral hydrogen atoms of about 10^9
g/s, a stellar wind with a velocity of 190 km/s and a temperature of ~10^5K.
An X-ray flare from the active star seen with Swift/XRT 8 hours before the
second-epoch observation supports the idea that the observed changes within the
upper atmosphere of the planet can be caused by variations in the stellar wind
properties, or by variations in the stellar energy input to the planetary
escaping gas (or a mix of the two effects). These observations provide the
first indication of interaction between the exoplanet's atmosphere and stellar
variations.Comment: To be published in A&A Letters, June 28, 201
HST/STIS Lyman-alpha observations of the quiet M dwarf GJ436: Predictions for the exospheric transit signature of the hot neptune GJ436b
Lyman-alpha (Lya) emission of neutral hydrogen (1215.67 Angstr\"om) is the
main contributor to the ultraviolet flux of low-mass stars such as M dwarfs. It
is also the main light source used in studies of the evaporating upper
atmospheres of transiting extrasolar planets with ultraviolet transmission
spectroscopy. However, there are very few observations of the Lya emissions of
quiet M dwarfs, and none exist for those hosting exoplanets. Here, we present
Lya observations of the hot-neptune host star GJ436 with the Hubble Space
Telescope Imaging Spectrograph (HST/STIS). We detect bright emission in the
first resolved and high quality spectrum of a quiet M dwarf at Lya. Using an
energy diagram for exoplanets and an N-body particle simulation, this detection
enables the possible exospheric signature of the hot neptune to be estimated as
a ~11% absorption in the Lya stellar emission, for a typical mass-loss rate of
10^10 g/s. The atmosphere of the planet GJ436b is found to be stable to
evaporation, and should be readily observable with HST. We also derive a
correlation between X-ray and Lya emissions for M dwarfs. This correlation will
be useful for predicting the evaporation signatures of planets transiting other
quiet M dwarfs.Comment: 8 pages, 8 figures, 2 tables. Accepted for publication in Astronomy &
Astrophysic
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