Seasonally stratified analyses of rainfall anomalies over the intra-Americas sea and surrounding land areas and of onset and end dates of the Central American rainy season show that the variability ...of the tropical Atlantic sea surface temperature anomaly (SSTA) is more strongly associated with rainfall over the Caribbean and Central America than is tropical eastern Pacific SSTA. Seasonal differences include the importance of antisymmetric configurations of tropical Atlantic SSTA in the dry season but not in the rainy season. Both oceans are related to rainfall, but the strength of the rainfall response appears to depend on how SSTA in the tropical Atlantic and eastern Pacific combine. The strongest response occurs when the tropical Atlantic is in the configuration of a meridional dipole (antisymmetric across the ITCZ) and the eastern tropical Pacific is of opposite sign to the tropical North Atlantic. When the tropical North Atlantic and tropical Pacific are of the same sign, the rainfall response is weaker. The rainy season in lower Central America tends to start early and end late in years that begin with warm SSTs in the tropical North Atlantic, and the end dates are also delayed when the eastern equatorial Pacific is cool. This enhancement of date departures for zonally antisymmetric configurations of SSTA between the North Atlantic and Pacific is qualitatively consistent with the results for rainfall anomalies.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Fractal Dimension of Projected Clouds Sánchez, Néstor; Alfaro, Emilio J; Pérez, Enrique
The Astrophysical journal,
06/2005, Letnik:
625, Številka:
2
Journal Article
Recenzirano
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The interstellar medium seems to have an underlying fractal structure, which can be characterized through its fractal dimension. However, interstellar clouds are observed as projected two-dimensional ...images, and the projection of a three-dimensional fractal distorts its measured properties. Here we use simulated fractal clouds to study the relationship between the three-dimensional fractal dimension (D sub(f)) of modeled clouds and the dimension resulting from their projected images. We analyze different fractal dimension estimators: the correlation and mass dimensions of the clouds and the perimeter-based dimension of their boundaries (D sub(per)). We find the functional forms relating D sub(f) with the projected fractal dimensions, as well as their dependence on the image resolution, which allow us to estimate the "real" D sub(f) value of a cloud from its projection. The application of these results to Orion A indicates in a self-consistent way that 2.5 D sub(f) 2.7 for this molecular cloud, a value higher than the result D sub(per) + 1 2.3 sometimes assumed in the literature for interstellar clouds.
Context. The Gaia-ESO Public Spectroscopic Survey is obtaining high-quality spectroscopy of some 100 000 Milky Way stars using the FLAMES spectrograph at the VLT, down to V = 19 mag, systematically ...covering all the main components of the Milky Way and providing the first homogeneous overview of the distributions of kinematics and chemical element abundances in the Galaxy. Observations of young open clusters, in particular, are giving new insights into their initial structure, kinematics, and their subsequent evolution. Aims. This paper describes the analysis of UVES and GIRAFFE spectra acquired in the fields of young clusters whose population includes pre-main sequence (PMS) stars. The analysis is applied to all stars in such fields, regardless of any prior information on membership, and provides fundamental stellar atmospheric parameters, elemental abundances, and PMS-specific parameters such as veiling, accretion, and chromospheric activity. Methods. When feasible, different methods were used to derive raw parameters (e.g. line equivalent widths) fundamental atmospheric parameters and derived parameters (e.g. abundances). To derive some of these parameters, we used methods that have been extensively used in the past and new ones developed in the context of the Gaia-ESO survey enterprise. The internal precision of these quantities was estimated by inter-comparing the results obtained by these different methods, while the accuracy was estimated by comparison with independent external data, such as effective temperature and surface gravity derived from angular diameter measurements, on a sample of benchmarks stars. A validation procedure based on these comparisons was applied to discard spurious or doubtful results and produce recommended parameters. Specific strategies were implemented to resolve problems of fast rotation, accretion signatures, chromospheric activity, and veiling. Results. The analysis carried out on spectra acquired in young cluster fields during the first 18 months of observations, up to June 2013, is presented in preparation of the first release of advanced data products. These include targets in the fields of the ρ Oph, Cha I, NGC 2264, γ Vel, and NGC 2547 clusters. Stellar parameters obtained with the higher resolution and larger wavelength coverage from UVES are reproduced with comparable accuracy and precision using the smaller wavelength range and lower resolution of the GIRAFFE setup adopted for young stars, which allows us to provide stellar parameters with confidence for the much larger GIRAFFE sample. Precisions are estimated to be ≈120 K rms in Teff, ≈0.3 dex rms in log g, and ≈0.15 dex rms in Fe/H for the UVES and GIRAFFE setups.
The nearby (distance ~ 350–400 pc), rich Vela OB2 association, includes γ2 Velorum, one of the most massive binaries in the solar neighbourhood and an excellent laboratory for investigating the ...formation and early evolution of young clusters. Recent Gaia-ESO survey observations have led to the discovery of two kinematically distinct populations in the young (10–15 Myr) cluster immediately surrounding γ2 Velorum. Here we analyse the results of Gaia-ESO survey observations of NGC 2547, a 35 Myr cluster located two degrees south of γ2 Velorum. The radial velocity distribution of lithium-rich pre-main sequence stars shows a secondary population that is kinematically distinct from and younger than NGC 2547. The radial velocities, lithium absorption lines, and the positions in a colour-magnitude diagram of this secondary population are consistent with those of one of the components discovered around γ2 Velorum. This result shows that there is a young, low-mass stellar population spread over at least several square degrees in the Vela OB2 association. This population could have originally been part of a cluster around γ2 Velorum that expanded after gas expulsion or formed in a less dense environment that is spread over the whole Vela OB2 region.
Context. The Li abundance observed in pre-main sequence and main sequence late-type stars is strongly age-dependent, but also shows a complex pattern depending on several parameters, such as ...rotation, chromospheric activity, and metallicity. The best way to calibrate these effects, and with the aim of studying Li as an age indicator for FGK stars, is to calibrate coeval groups of stars, such as open clusters (OCs) and associations. Aims. We present a considerable target sample of 42 OCs and associations – with an age range from 1 Myr to 5 Gyr – observed within the Gaia-ESO survey (GES), and using the latest data provided by GES iDR6 and the most recent release of Gaia that was then available, EDR3. As part of this study, we update and improve the membership analysis for all 20 OCs presented in our previous article. Methods. We perform detailed membership analyses for all target clusters to identify likely candidates, using all available parameters provided by GES, complemented with detailed bibliographical searches, and based on numerous criteria: from radial velocity distributions, to the astrometry (proper motions and parallaxes) and photometry provided by Gaia, to gravity indicators (log g and the γ index), Fe/H metallicity, and Li content in diagrams of (Li equivalent widths) EW(Li) versus Teff. Results. We obtain updated lists of cluster members for the whole target sample, as well as a selection of Li-rich giant contaminants obtained as an additional result of the membership process. Each selection of cluster candidates was thoroughly contrasted with numerous existing membership studies using data from Gaia to ensure the most robust results. Conclusions. These final cluster selections will be used in the third and last paper of this series, which reports the results of a comparative study characterising the observable Li dispersion in each cluster and analysing its dependence on several parameters, allowing us to calibrate a Li–age relation and obtain a series of empirical Li envelopes for key ages in our sample.
The main objective of this study is the characterization of the velocity field in the Cygnus OB1 association using the radial velocity data currently available in the literature. This association is ...part of a larger star-forming complex located in the direction of the Cygnus region, but whose main subsystems may be distributed at different distances from the sun. We have collected radial velocity data for more than 300 stars in the area of 5 x 5 deg2 centred on the Cygnus OB1 association. We present the results of a kinematic clustering analysis in the subspace of the phase space formed by angular coordinates and radial velocity using two independent methodologies. We have found evidence of structure in the phase space with the detection of two main groups, corresponding to different radial velocity and distance values, belonging to the association, and associated with two main shells defined by the Ha emission. A third grouping well separated from the other two in velocity appears to occupy the whole region associated with what has been called 'common shell'.
Context. The Gaia-ESO Survey (GES) is a large public spectroscopic survey at the European Southern Observatory Very Large Telescope. Aims. A key aim is to provide precise radial velocities (RVs) and ...projected equatorial velocities (vsini) for representative samples of Galactic stars, which will complement information obtained by the Gaia astrometry satellite. Methods. We present an analysis to empirically quantify the size and distribution of uncertainties in RV and vsini using spectra from repeated exposures of the same stars. Results. We show that the uncertainties vary as simple scaling functions of signal-to-noise ratio (S/N) and vsini, that the uncertainties become larger with increasing photospheric temperature, but that the dependence on stellar gravity, metallicity and age is weak. The underlying uncertainty distributions have extended tails that are better represented by Student’s t-distributions than by normal distributions. Conclusions. Parametrised results are provided, which enable estimates of the RV precision for almost all GES measurements, and estimates of the vsini precision for stars in young clusters, as a function of S/N, vsini and stellar temperature. The precision of individual high S/N GES RV measurements is 0.22–0.26 km s-1, dependent on instrumental configuration.
Las parasitosis gastrointestinales en bovinos de producción son uno de los problemas sanitarios más importantes a nivel mundial. Estos nematodos ocasionan problemas gastroentéricos que se ...caracterizan clínicamente por diarrea, debilidad, hemorragias y deshidratación. Entre las parasitosis gastrointestinales causadas por nematodos en ganado bovino, se destacan las familias: Trichuridae, Trichostrongylidae, Ancylostomidae, Ascaridae y Strongyloididae. El propósito de esta investigación fue determinar la eficacia de las distintas técnicas coproparasitológicas cualitativas y cuantitativas para la detección de nematodos gastrointestinales en ganado bovino. Para este estudio se utilizaron 250 muestras de vacas de raza carnicera, divididos en diferentes grupos, para la aplicación de las técnicas coproparasitológicas de tipo cualitativo y cuantitativo, los cuales fueron escogidos específicamente teniendo en cuenta criterios de inclusión y exclusión para cada animal. Los resultados entregados por este estudio indicaron que el mayor porcentaje en la identificación de estados infectantes parasitarios fue por medio de las técnicas coproparasitologicas de tipo cualitativo, principalmente aquellas de flotación de sulfato de zinc y magnesio con un 50%.
We report magnetic and spectroscopic observations and modelling of the Of?p star CPD -28... 2561. Using more than 75 new spectra, we have measured the equivalent width variations and examined the ...dynamic spectra of photospheric and wind-sensitive spectral lines. A period search results in an unambiguous 73.41 d variability period. High-resolution spectropolarimetric data analysed using least-squares deconvolution yield a Zeeman signature detected in the mean Stokes V profile corresponding to phase 0.5 of the spectral ephemeris. Interpreting the 73.41 d period as the stellar rotational period, we have phased the equivalent widths and inferred longitudinal field measurements. The phased magnetic data exhibit a weak sinusoidal variation, with maximum of about 565 G at phase 0.5, and a minimum of about -335 G at phase 0.0, with extrema approximately in phase with the (double-wave) H... equivalent width variation. Modelling of the H... equivalent width variation assuming a quasi-3D magnetospheric model produces a unique solution for the ambiguous couplet of inclination and magnetic obliquity angles: (i, ...) or (..., i) = (35..., 90...). Adopting either geometry, the longitudinal field variation yields a dipole polar intensity Bd = 2.6 ± 0.9 kG, consistent with that obtained from direct modelling of the Stokes V profiles. We derive a wind magnetic confinement parameter ..., leading to an Alfven radius ..., and a Kepler radius ... This supports a physical scenario in which the H... emission and other line variability have their origin in an oblique, corotating 'dynamical magnetosphere' structure resulting from a magnetically channelled wind. Nevertheless, the details of the formation of spectral lines and their variability within this framework remain generally poorly understood. (ProQuest: ... denotes formulae/symbols omitted.)
The effect of 2-chlorophenol (2-CP) on ammonium and nitrite-oxidizing processes was kinetically evaluated in batch cultures with nitrifying sludge at steady state. Assays with ammonium or nitrite as ...energy source and 2.5, 5.0, or 10.0 mg 2-CP-C/l were conducted. Control assays without 2-CP were also performed. Ammonium-oxidizing activity was completely inhibited at the different 2-CP concentrations, whereas nitrite-oxidizing activity was present as nitrite was completely consumed and converted to nitrate irrespectively of 2-CP concentration. In the presence of 2.5 and 5.0 mg 2-CP-C/l, no significant effect on specific rates of nitrite consumption and nitrate production was observed, but a significant decrease on these parameters was observed at 10.0 mg 2-CP-C/l. The nitrifying sludge previously exposed to 2-CP was unable to completely recover its ammonium and nitrite oxidation capacity. Nevertheless, complete 2-CP consumption was achieved in all assays. The effect of 2-CP on ammonium oxidation was observed at kinetic and metabolic pathway level, whereas the effect on nitrite oxidation was observed only at kinetic level. The results obtained in this work evidenced that in order to achieve a successful nitrification process the presence in wastewater of even 2.5 mg 2-CP-C/l should be avoided.
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