An Upper Limit on the Mass of the Circumplanetary Disk for DH Tau b

Indexación: Scopus.DH Tau is a young (sim;1 Myr) classical T Tauri star. It is one of the few young PMS stars known to be associated with a planetary mass companion, DH Tau b, orbiting at large separation and detected by direct imaging. DH Tau b is thought to be accreting based on copious Ha emission and exhibits variable Paschen Beta emission. NOEMA observations at 230 GHz allow us to place constraints on the disk dust mass for both DH Tau b and the primary in a regime where the disks will appear optically thin. We estimate a disk dust mass for the primary, DH Tau A of 17.2 ± 1.7 MÅ, which gives a disk to star mass ratio of 0.014 (assuming the usual gas to dust mass ratio of 100 in the disk). We find a conservative disk dust mass upper limit of 0.42M⊕ for DH Tau b, assuming that the disk temperature is dominated by irradiation from DH Tau b itself. Given the environment of the circumplanetary disk, variable illumination from the primary or the equilibrium temperature of the surrounding cloud would lead to even lower disk mass estimates. A MCFOST radiative transfer model, including heating of the circumplanetary disk by DH Tau b and DH Tau A, suggests that a mass-averaged disk temperature of 22 K is more realistic, resulting in a dust disk mass upper limit of 0.09M⊕ for DH Tau b. We place DH Tau b in context with similar objects and discuss the consequences for planet formation models.http://iopscience.iop.org/article/10.3847/1538-3881/aa74cd/met

Petrology of Matthew and Hunter volcanoes, South New Hebrides island arc (Southwest Pacific)

Matthew and Hunter, the two southernmost active volcanoes of the New Hebrides island arc (southwest Pacific) differ markedly from the other (mainly tholeitic) Quaternary volcanoes of this arc. Geodynamically related to the New Hebrides subduction zone, they also lie close to the southern limb of the active expanding ridge of the North Fiji Basin. Both volcanoes are made up of acid, medium-K, calcalkaline orogenic andesites, containing a variety of inclusions (pyroxene- and gabbroic cumulates, as well as doleritic cognate inclusions). This paper presents the first systematic petrographic and chemical study of these volcanics and their inclusions. Trace-element geochemistry and rare-earth element modelling suggest that the two volcanoes developed from successive batches of similar parental magmas, originating from limited partial fusion of garnet peridotite in the mantle wedge. Various degrees of fractional crystallization ot these batches led to the formation of three volcanic suites: Hunter (little fractionated), West-Matthew (moderately fractionated) and East-Matthew (highly fractionated). Moreover, on Matthew island, no correlation exists between the degree of fractionation and the eruptive chronology, the youngest edifice (West-Matthew) being less evolved than the older on (East-Matthew). (Résumé d'auteur

Investigations of OTR screen surfaces and shapes

Optical transition radiation (OTR) has proven to be a flexible and effective tool for measuring a wide range of beam parameters, in particular the beam divergence and the transverse beam profile. It is today an established and widely used diagnostic method providing linear real-time measurements. Measurements in the CLIC Test Facility (CTF3) showed that the performance of the present profile monitors is limited by the optical acceptance of the imaging system. In this paper, two methods to improve the systems' performance are presented and results from measurements are shown. First, the influence of the surface quality of the OTR screen itself is addressed. Several possible screen materials have been tested to which different surface treatment techniques were applied. Results from the measured optical characteristics are given. Second, a parabolic-shaped screen support was investigated with the aim of providing an initial focusing of the emitted radiation and thus to reduce the problem of aperture limitation

Combining causal model and focus group discussions experiences learned from a socio-anthropological research on the differing perceptions of caretakers and health professionals on children's health (Bolivia/Peru)

The paper discusses the utility of constructing causal models in focus groups. This was experienced as a complement to an in-depth ethnographic research on the differing perceptions of caretakers and health professionals on child's growth and development in Peru and Bolivia. The rational, advantages, difficulties and necessary adaptations of combining the two techniques are discussed on the basis of concrete examples. Authors conclude that the building of a causal model in a focus group session can be useful in comparing lay etiologies of diseases as perceived by different categories of caretakers and health professionals and in identifying specific health risks faced by children. Causal model building in a focus group can help renew discussions and participants'interest but its use is only justified when the study concerns the perception of the causality of a given phenomenon

Estimation of the oceanic pCO₂ in the North Atlantic from VOS lines in-situ measurements: parameters needed to generate seasonally mean maps

Automated instruments on board Volunteer Observing Ships (VOS) have provided high-frequency pCO₂ measurements over basin-wide regions for a decade or so. In order to estimate regional air-sea CO₂ fluxes, it is necessary to interpolate between in-situ measurements to obtain maps of the marine pCO₂. Such an interpolation remains, however, a difficult task because VOS lines are too distant from each other to capture the high pCO₂ variability. Relevant physical parameters available at large scale are thus necessary to serve as a guide to estimate the pCO₂ values between the VOS lines. Satellites do not measure pCO₂ but they give access to parameters related to the processes that control its variability, such as sea surface temperature (SST). In this paper we developed a method to compute pCO₂ maps using satellite data (SST and CHL, the chlorophyll concentration), combined with a climatology of the mixed-layer depth (MLD). Using 15 401 measurements of surface pCO₂ acquired in the North Atlantic between UK and Jamaica, between June 1994 and August 1995, we show that the parameterization of pCO₂ as a function of SST, CHL and MLD yields more realistic pCO₂ values than parameterizations that have been widely used in the past, based on SST, latitude, longitude or SST only. This parameterization was then used to generate seasonal maps of pCO₂ over the North Atlantic. Results show that our approach yields the best marine pCO₂ estimates, both in terms of absolute accuracy, when compared with an independent data set, and of geographical patterns, when compared to the climatology of Takahashi et al. (2002). This suggests that monitoring the seasonal variability of pCO₂ over basin-wide regions is possible, provided that sufficient VOS lines are available

Segmented Beam Dump for Time Resolved Spectrometry on a High Current Electron Beam

In the CLIC Test Facility 3 (CTF3), the strong coupling between the beam and the accelerating cavities induces transient effects such that the head of the pulse is accelerated twice as much as the rest of the pulse. Three spectrometer lines are installed along the linac with the aim of measuring energy spread versus time with a 20ns resolution. A major difficulty is due to the high power carried by the beam which imposes extreme constraints of thermal and radiation resistances on the detector. This paper presents the design and the performances of a simple and easy-to-maintain device, called âsegmented dump'. In this device, the particles are stopped inside metallic plates and the deposited charge is measured in the same way as in Faraday cups. Simulations were carried out with the Monte Carlo code âFLUKA' to evaluate the problems arising from the energy deposition and to find ways to prevent or reduce them. The detector resolution was optimized by an adequate choice of material and thickness of the plates. The overall layout of the monitor is described with special emphasis on its mechanical assembly. Finally, limitations arising at higher beam energies are discussed

Grain size limits derived from 3.6 {\mu}m and 4.5 {\mu}m coreshine

Recently discovered scattered light from molecular cloud cores in the wavelength range 3-5 {\mu}m (called "coreshine") seems to indicate the presence of grains with sizes above 0.5 {\mu}m. We aim to analyze 3.6 and 4.5 {\mu}m coreshine from molecular cloud cores to probe the largest grains in the size distribution. We analyzed dedicated deep Cycle 9 Spitzer IRAC observations in the 3.6 and 4.5 {\mu}m bands for a sample of 10 low-mass cores. We used a new modeling approach based on a combination of ratios of the two background- and foreground-subtracted surface brightnesses and observed limits of the optical depth. The dust grains were modeled as ice-coated silicate and carbonaceous spheres. We discuss the impact of local radiation fields with a spectral slope differing from what is seen in the DIRBE allsky maps. For the cores L260, ecc806, L1262, L1517A, L1512, and L1544, the model reproduces the data with maximum grain sizes around 0.9, 0.5, 0.65, 1.5, 0.6, and > 1.5 {\mu}m, respectively. The maximum coreshine intensities of L1506C, L1439, and L1498 in the individual bands require smaller maximum grain sizes than derived from the observed distribution of band ratios. Additional isotropic local radiation fields with a spectral shape differing from the DIRBE map shape do not remove this discrepancy. In the case of Rho Oph 9, we were unable to reliably disentangle the coreshine emission from background variations and the strong local PAH emission. Considering surface brightness ratios in the 3.6 and 4.5 {\mu}m bands across a molecular cloud core is an effective method of disentangling the complex interplay of structure and opacities when used in combination with observed limits of the optical depth.Comment: 23 pages, 18 figures, accepted for publication in A&

Massive Increase, Spread, and Exchange of Extended Spectrum {beta}-Lactamase-Encoding Genes Among Intestinal Enterobacteriaceae in Hospitalized Children With Severe Acute Malnutrition in Niger.

Background. From the time of CTX-M emergence, extended-spectrum β-lactamase-producing enterobacteria (ESBL-E) have spread worldwide in community settings as well as in hospitals, particularly in developing countries. Although their dissemination appears linked to Escherichia coli intestinal carriage, precise paths of this dynamic are largely unknown. Methods. Children from a pediatric renutrition center were prospectively enrolled in a fecal carriage study. Antibiotic exposure was recorded. ESBL-E strains were isolated using selective media from fecal samples obtained at admission and, when negative, also at discharge. ESBL-encoding genes were identified, their environments and plasmids were characterized, and clonality was assessed with polymerase chain reaction-based methods and pulsed-field gel electrophoresis for E. coli and Klebsiella pneumoniae. E. coli strains were subjected to multilocus sequence typing. Results. The ESBL-E carriage rate was 31% at admission in the 55 children enrolled. All children enrolled received antibiotics during hospitalization. Among the ESBL-E-negative children, 16 were resampled at discharge, and the acquisition rate was 94%. The bla(CTX-M-15) gene was found in >90% of the carriers. Genetic environments and plasmid characterization evidenced the roles of a worldwide, previously described, multidrug-resistant region and of IncF plasmids in CTX-M-15 E. coli dissemination. Diversity of CTX-M-15-carrying genetic structures and clonality of acquired ESBL E. coli suggested horizontal genetic transfer and underlined the potential of some ST types for nosocomial cross-transmission. Conclusions. Cross-transmission and high selective pressure lead to very high acquisition of ESBL-E carriage, contributing to dissemination in the community. Strict hygiene measures as well as careful balancing of benefit-risk ratio of current antibiotic policies need to be reevaluated