1,772 research outputs found

    Dependable Distributed Computing for the International Telecommunication Union Regional Radio Conference RRC06

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    The International Telecommunication Union (ITU) Regional Radio Conference (RRC06) established in 2006 a new frequency plan for the introduction of digital broadcasting in European, African, Arab, CIS countries and Iran. The preparation of the plan involved complex calculations under short deadline and required dependable and efficient computing capability. The ITU designed and deployed in-situ a dedicated PC farm, in parallel to the European Organization for Nuclear Research (CERN) which provided and supported a system based on the EGEE Grid. The planning cycle at the RRC06 required a periodic execution in the order of 200,000 short jobs, using several hundreds of CPU hours, in a period of less than 12 hours. The nature of the problem required dynamic workload-balancing and low-latency access to the computing resources. We present the strategy and key technical choices that delivered a reliable service to the RRC06

    X-Shooter study of accretion in ρ\rho-Ophiucus: very low-mass stars and brown dwarfs

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    We present new VLT/X-Shooter optical and NIR spectra of a sample of 17 candidate young low-mass stars and BDs in the rho-Ophiucus cluster. We derived SpT and Av for all the targets, and then we determined their physical parameters. All the objects but one have M*<0.6 Msun, and 8 have mass below or close to the hydrogen-burning limit. Using the intensity of various emission lines present in their spectra, we determined the Lacc and Macc for all the objects. When compared with previous works targeting the same sample, we find that, in general, these objects are not as strongly accreting as previously reported, and we suggest that the reason is our more accurate estimate of the photospheric parameters. We also compare our findings with recent works in other slightly older star-forming regions to investigate possible differences in the accretion properties, but we find that the accretion properties for our targets have the same dependence on the stellar and substellar parameters as in the other regions. This leads us to conclude that we do not find evidence for a different dependence of Macc with M* when comparing low-mass stars and BDs. Moreover, we find a similar small (1 dex) scatter in the Macc-M* relation as in some of our recent works in other star-forming regions, and no significant differences in Macc due to different ages or properties of the regions. The latter result suffers, however, from low statistics and sample selection biases in the current studies. The small scatter in the Macc-M* correlation confirms that Macc in the literature based on uncertain photospheric parameters and single accretion indicators, such as the Ha width, can lead to a scatter that is unphysically large. Our studies show that only broadband spectroscopic surveys coupled with a detailed analysis of the photospheric and accretion properties allows us to properly study the evolution of disk accretion rates.Comment: accepted for publication in Astronomy & Astrophysics. Abstract shortened to fit arXiv constraint

    Searching for physics beyond the Standard Model in the decay B+ -> K+K+pi-

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    The observation potential of the decay B+ -> K+K+pi- with the ATLAS detector at LHC is described in this paper. In the Standard Model this decay mode is highly suppressed, while in models beyond the Standard Model it could be significantly enhanced. To improve the selection of the K+K+pi- final state, a charged hadron identification using Time-over-Threshold measurements in the ATLAS Transition Radiation Tracker was developed and used.Comment: 12 pages, 4 figures, 1 tabl

    An extensive VLT/X-Shooter library of photospheric templates of pre-main sequence stars

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    Studies of the formation and evolution of young stars and their disks rely on the knowledge of the stellar parameters of the young stars. The derivation of these parameters is commonly based on comparison with photospheric template spectra. Furthermore, chromospheric emission in young active stars impacts the measurement of mass accretion rates, a key quantity to study disk evolution. Here we derive stellar properties of low-mass pre-main sequence stars without disks, which represent ideal photospheric templates for studies of young stars. We also use these spectra to constrain the impact of chromospheric emission on the measurements of mass accretion rates. The spectra in reduced, flux-calibrated, and corrected for telluric absorption form are made available to the community. We derive the spectral type for our targets by analyzing the photospheric molecular features present in their VLT/X-Shooter spectra by means of spectral indices and comparison of the relative strength of photospheric absorption features. We also measure effective temperature, gravity, projected rotational velocity, and radial velocity from our spectra by fitting them with synthetic spectra with the ROTFIT tool. The targets have negligible extinction and spectral type from G5 to M8. We perform synthetic photometry on the spectra to derive the typical colors of young stars in different filters. We measure the luminosity of the emission lines present in the spectra and estimate the noise due to chromospheric emission in the measurements of accretion luminosity in accreting stars. We provide a calibration of the photospheric colors of young PMS stars as a function of their spectral type in a set of standard broad-band optical and near-infrared filters. For stars with masses of ~ 1.5Msun and ages of ~1-5 Myr, the chromospheric noise converts to a limit of measurable mass accretion rates of ~ 3x10^-10 Msun/yr.Comment: Accepted for publication on Astronomy & Astrophysics. The spectra of the photospheric templates will be uploaded to Vizier, but are already available on request. Abstract shortened for arxiv constraints. Language edited versio

    Mapping young stellar populations towards Orion with Gaia DR1

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    We use the first data release of the Gaia mission to explore the three dimensional arrangement and the age ordering of the many stellar groups towards the Orion OB association, aiming at a new classification and characterization of the stellar population. We make use of the parallaxes and proper motions provided in the Tycho Gaia Astrometric Solution (TGAS) sub-set of the Gaia catalogue, and of the combination of Gaia and 2MASS photometry. In TGAS we find evidence for the presence of a young population, at a parallax ϖ∌2.65 mas\varpi \sim 2.65 \, \mathrm{mas}, loosely distributed around some known clusters: 25 Ori, Ï”\epsilon Ori and σ\sigma Ori, and NGC 1980 (Îč\iota Ori). The low mass counterpart of this population is visible in the color-magnitude diagrams constructed by combining Gaia and 2MASS photometry. We study the density distribution of the young sources in the sky. We find the same groups as in TGAS, and also some other density enhancements that might be related to the recently discovered Orion X group, the Orion dust ring, and to the λ\lambda Ori complex. We estimate the ages of this population and we infer the presence of an age gradient going from 25 Ori (13-15 Myr) to the ONC (1-2 Myr). We confirm this age ordering by repeating the Bayesian fit using the Pan-STARRS1 data. The estimated ages towards the NGC 1980 cluster span a broad range of values. This can either be due to the presence of two populations coming from two different episodes of star formation or to a large spread along the line of sight of the same population. Our results form the first step towards using the Gaia data to unravel the complex star formation history of the Orion region in terms of the different star formation episodes, their duration, and their effects on the surrounding interstellar medium.Comment: 17 pages, 17 figure

    Urbanization effect on trends in sunshine duration in China

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    There is an ongoing debate on whether the observed decadal variations in surface solar radiation, known as "dimming" and "brightening" periods, are a large-scale or solely local phenomenon. We investigated this issue using long-term sunshine duration records from China, which experienced a rapid increase in urbanization during the past decades. Over the period 1960–2013, 172 pairs of urban and nearby rural stations were analyzed. Urban and rural sunshine duration trends show similar spatial patterns during a dimming phase (1960–1989) and a subsequent period during which trends were leveling off (1990–2013). This indicates that rather than local effects, the trends in sunshine duration are on more of a national or regional scale in China. Nevertheless, in the dimming phase, the declining rate of sunshine duration in rural areas is around two-thirds of that in urban areas. The ratio of rural to urban dimming generally increases from a minimum of 0.39 to a maximum of 0.87 with increasing indices of urbanization calculated based on the year 2013. It reaches a maximum when the urbanization level exceeds 50 %, the urban population exceeds 20 million, or the population density becomes higher than 250 person km−2. After the transition into the leveling-off period, sunshine duration trends are no longer significantly affected by urbanization. Meanwhile, the number of laws and regulations related to air pollution and investment in pollution treatment have been increasing in China.ISSN:0992-7689ISSN:0939-4176ISSN:1432-057

    On the gas content of transitional disks: a VLT/X-Shooter study of accretion and winds

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    Transitional disks (TDs) are thought to be a late evolutionary stage of protoplanetary disks with dust depleted inner regions. The mechanism responsible for this depletion is still under debate. To constrain the models it is mandatory to have a good understanding of the properties of the gas content of the inner disk. Using X-Shooter broad band -UV to NIR- medium resolution spectroscopy we derive the stellar, accretion, and wind properties of a sample of 22 TDs. The analysis of these properties allows us to put strong constraints on the gas content in a region very close to the star (<0.2 AU) which is not accessible with any other observational technique. We fit the spectra with a self-consistent procedure to derive simultaneously SpT,Av,and mass accretion rates (Macc) of the targets. From forbidden emission lines we derive the wind properties of the targets. Comparing our findings to values for cTTs, we find that Macc and wind properties of 80% of the TDs in our sample, which is strongly biased towards strongly accreting objects, are comparable to those of cTTs. Thus, there are (at least) some TDs with Macc compatible with those of cTTs, irrespective of the size of the dust inner hole.Only in 2 cases Macc are much lower, while the wind properties are similar. We do not see any strong trend of Macc with the size of the dust depleted cavity, nor with the presence of a dusty optically thick disk close to the star. In the TDs in our sample there is a gas rich inner disk with density similar to that of cTTs disks. At least for some TDs, the process responsible of the inner disk clearing should allow for a transfer of gas from the outer disk to the inner region. This should proceed at a rate that does not depend on the physical mechanism producing the gap seen in the dust emission and results in a gas density in the inner disk similar to that of unperturbed disks around stars of similar mass.Comment: Accepted on Astronomy & Astrophysics. Abstract shortened to fit arXiv constraint

    Time-resolved photometry of the young dipper RX~J1604.3-2130A:Unveiling the structure and mass transport through the innermost disk

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    Context. RX J1604.3-2130A is a young, dipper-type, variable star in the Upper Scorpius association, suspected to have an inclined inner disk, with respect to its face-on outer disk. Aims. We aim to study the eclipses to constrain the inner disk properties. Methods. We used time-resolved photometry from the Rapid Eye Mount telescope and Kepler 2 data to study the multi-wavelength variability, and archival optical and infrared data to track accretion, rotation, and changes in disk structure. Results. The observations reveal details of the structure and matter transport through the inner disk. The eclipses show 5 d quasi-periodicity, with the phase drifting in time and some periods showing increased/decreased eclipse depth and frequency. Dips are consistent with extinction by slightly processed dust grains in an inclined, irregularly-shaped inner disk locked to the star through two relatively stable accretion structures. The grains are located near the dust sublimation radius (similar to 0.06 au) at the corotation radius, and can explain the shadows observed in the outer disk. The total mass (gas and dust) required to produce the eclipses and shadows is a few % of a Ceres mass. Such an amount of mass is accreted/replenished by accretion in days to weeks, which explains the variability from period to period. Spitzer and WISE infrared variability reveal variations in the dust content in the innermost disk on a timescale of a few years, which is consistent with small imbalances (compared to the stellar accretion rate) in the matter transport from the outer to the inner disk. A decrease in the accretion rate is observed at the times of less eclipsing variability and low mid-IR fluxes, confirming this picture. The v sin i = 16 km s(-1) confirms that the star cannot be aligned with the outer disk, but is likely close to equator-on and to be aligned with the inner disk. This anomalous orientation is a challenge for standard theories of protoplanetary disk formation.Science & Technology Facilities Council (STFC): ST/S000399/1. ESO fellowship. European Union (EU): 823 823. German Research Foundation (DFG): FOR 2634/1 TE 1024/1-1. French National Research Agency (ANR): ANR-16-CE31-0013. Alexander von Humboldt Foundation. European Research Council (ERC): 678 194. European Research Council (ERC): 742 095. National Aeronautics & Space Administration (NASA). National Science Foundation (NSF). National Aeronautics & Space Administration (NASA): NNG05GF22G. National Science Foundation (NSF): AST-0909182, AST-1 313 422

    X-Shooter spectroscopy of young stellar objects in Lupus. Atmospheric parameters, membership and activity diagnostics

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    A homogeneous determination of basic stellar parameters of young stellar object (YSO) candidates is needed to confirm their evolutionary stage, membership to star forming regions (SFRs), and to get reliable values of the quantities related to chromospheric activity and accretion. We used the code ROTFIT and synthetic BT-Settl spectra for the determination of the atmospheric parameters (Teff and logg), the veiling, the radial (RV) and projected rotational velocity (vsini), from X-Shooter spectra of 102 YSO candidates in the Lupus SFR. We have shown that 13 candidates can be rejected as Lupus members based on their discrepant RV with respect to Lupus and/or the very low logg values. At least 11 of them are background giants. The spectral subtraction of inactive templates enabled us to measure the line fluxes for several diagnostics of both chromospheric activity and accretion. We found that all Class-III sources have Hα\alpha fluxes compatible with a pure chromospheric activity, while objects with disks lie mostly above the boundary between chromospheres and accretion. YSOs with transitional disks displays both high and low Hα\alpha fluxes. We found that the line fluxes per unit surface are tightly correlated with the accretion luminosity (LaccL_{\rm acc}) derived from the Balmer continuum excess. This rules out that the relationships between LaccL_{\rm acc} and line luminosities found in previous works are simply due to calibration effects. We also found that the CaII-IRT flux ratio, F8542/F8498F_{8542}/F_{8498}, is always small, indicating an optically thick emission source. The latter can be identified with the accretion shock near the stellar photosphere. The Balmer decrement reaches instead, for several accretors, high values typical of optically thin emission, suggesting that the Balmer emission originates in different parts of the accretion funnels with a smaller optical depth.Comment: 28 pages, 26 figures, accepted by A&

    Neurological determination of death in isolated brainstem lesions: A case report to highlight the issues involved

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    The neurological determination of death in patients with isolated brainstem lesions or by disruption of the posterior cerebral circulation is uncommon and many intensivists may never see such a case in their career. It is also the only major difference between the “whole brain” and “brain stem” formulations for the neurological determination of death. We present a case of a patient with infarction of the structures supplied by the posterior cerebral circulation in whom death was diagnosed using neurological criteria, to illustrate the issues involved. We also suggest that international consensus may be achieved if ancillary tests, such as CT angiography, are made mandatory in this situation o demonstrate loss of blood flow in the anterior cerebral circulation as well the posterior circulation
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