Determining the Physical Properties of the B Stars I. Methodology and First Results

We describe a new approach to fitting the UV-to-optical spectra of B stars to model atmospheres and present initial results. Using a sample of lightly reddened stars, we demonstrate that the Kurucz model atmospheres can produce excellent fits to either combined low dispersion IUE and optical photometry or HST FOS spectrophotometry, as long as the following conditions are fulfilled: 1) an extended grid of Kurucz models is employed, 2) the IUE NEWSIPS data are placed on the FOS absolute flux system using the Massa & Fitzpatrick (1999) transformation, and 3) all of the model parameters and the effects of interstellar extinction are solved for simultaneously. When these steps are taken, the temperatures, gravities, abundances and microturbulence velocities of lightly reddened B0-A0 V stars are determined to high precision. We also demonstrate that the same procedure can be used to fit the energy distributions of stars which are reddened by any UV extinction curve which can be expressed by the Fitzpatrick & Massa (1990) parameterization scheme. We present an initial set of results and verify our approach through comparisons with angular diameter measurements and the parameters derived for an eclipsing B star binary. We demonstrate that the metallicity derived from the ATLAS 9 fits to main sequence B stars is essentially the Fe abundance. We find that a near zero microturbulence velocity provides the best-fit to all but the hottest or most luminous stars (where it may become a surrogate for atmospheric expansion), and that the use of white dwarfs to calibrate UV spectrophotometry is valid.Comment: 17 pages, including 2 pages of Tables and 6 pages of Figures. Astrophysical Jounral, in pres

Characterizing the magnetic fields of the first tau Sco analogues

The B0.2 V magnetic star tau Sco stands out from the larger population of massive OB stars due to its high X-ray activity, peculiar wind diagnostics and complex magnetic field. Recently, Petit et al. 2011 presented the discovery of the first two tau Sco analogues -- HD 66665 and HD 63425, identified by the striking similarity of their UV spectra to that of tau Sco. ESPaDOnS and Narval spectropolarimetric observations were obtained by the Magnetism in Massive Stars CFHT and TBL Large Programs, in order to characterize the stellar and magnetic properties of these stars. A magnetic field of similar surface strength was found on both stars, reinforcing the connection between the presence of a magnetic field and wind peculiarities. We present additional phase-resolved observations secured by the MiMeS collaboration for HD 66665 in order to measure its magnetic geometry, and correlate that geometry with diagnostics of mass-loss.Comment: to appear in the proceedings of Stellar polarimetry: From birth to death, Madison, USA, June 27 - June 30, 2011 (version 2 was updated to correct a typo in the arXiv metadata

Far-UV FUSE spectroscopy of the OVI resonance doublet in Sand2 (WO)

We present Far-Ultraviolet Spectroscopic Explorer (FUSE) spectroscopy of Sand 2, a LMC WO-type Wolf-Rayet star, revealing the OVI resonance P Cygni doublet at 1032-38A. These data are combined with HST/FOS ultraviolet and Mt Stromlo 2.3m optical spectroscopy, and analysed using a spherical, non-LTE, line-blanketed code. Our study reveals exceptional stellar parameters: T*=150,000K, v_inf=4100 km/s, log (L/Lo)=5.3, and Mdot=10^-5 Mo/yr if we adopt a volume filling factor of 10%. Elemental abundances of C/He=0.7+-0.2 and O/He=0.15(-0.05+0.10) by number qualitatively support previous recombination line studies. We confirm that Sand 2 is more chemically enriched in carbon than LMC WC stars, and is expected to undergo a supernova explosion within the next 50,000 yr.Comment: 17 pages, 4 figures, AASTeX preprint format. This paper will appear in a special issue of ApJ Letters devoted to the first scientific results from the FUSE missio

Evaluación de una población clonal de Tetrachne dregei Nees. II. Profundidad y sistema de siembra

Evaluation of a clonal population of Tetrachne dregei Nees. n. Depth and sowing method. The main limitation for the extensive cultivation of Tetrachne dregei Nees is the difficulty to obtain its establishment. The purpose of this work was to determine the appropriate sowing depth, and to compare sowing and compactation methods. In plastic trays with sterilized soil under controlled photo and thermoperiod, emergency curves were obtained for anthecium and caryopsis sowed at different depth. Results were analized by Tukey test and regression. It were compared five sowing methods, with a common distribution system. Emergence percentage was never smaller than 50% for anthecium and caryopsis sowed between O and 2 cm. deep. Ploughing and line compactation showed to be the best treatment to obtain tetracne establishment. Degree and type of weeds had an adverse effect on its establishment.La dificultad para lograr su implantación es la Iimitante principal para el cultivo extensivo de Tetracnne dregei Nees. El propósito del presente trabajo fue determinar la profundidad apropiada de siembra, y comparar métodos mecanizados de siembra y compactación. Se obtuvieron las curvas de emergencia de antecios y cariopses correspondientes a distintas profundidades de siembra, trabajando con bandejas plásticas provistas de tierra esterilizada y bajo condiciones controladas de termo y fotoperíodo. Los resultados se examinaron por análisis de variancia y regresión. Se compararon cinco métodos de siembra, con un único sistema de distribución (al voleo). Para antecios y cariopses "pesados" se determinó una emergencia no menor al 50% para profundidades comprendidas entre 0,0 y 2,0 cm. de la superficie. La remoción previa del suelo y la posterior compactación en líneas permitieron un establecimiento adecuado del cultivo. El grado y la composición del enmalezamiento incidieron negativamente en el establecimiento de las plantas

Evaluación de una población clonal de Tetrachne dregei Nees. Germinación de antecios y cariopses

lnformation about Tetrachne dregei Nees as a cultivated pasture is not available. The main purpose of this work was to determine the germination percentage (G.P.) of Tetracne disseminules under different treatments - Le. Physicals (pre- chilling and pre-washíng), hormonals (plant hormones: AG 3, CCC, ANA) and not-treated controls. Germination tests were performed on petri dishes in growth chamber with controlled photo and thermoperiod. Tukey test was used for mean significance differences. Higher G.P. was obtained from heavier caryopsis. Germination at 48 hours of caryopsis Oight and heavy) excessed that of the anthecium. Treatments didn't enhance G.P. of anthecium and caryopsis. Leaves and root development of seedlings were affected by growing regulators.Tetrachne dregei Nees es una gramínea forrajera promisoria para la región templada semiárida. Como pastura cultivada no se registran antecedentes, lo que determina la necesidad de generar información que posibilite su incorporación al cultivo extensivo. Se analizó la germinación de antecios y cariopses a partir del efecto que ejercen tratamientos físicos (pre-enfriado y pre-Iavado y con reguladores hormonales (ácido giberélico, CCC, y ANA). Las siembras se efectuaron en placas de Petri, bajo condiciones controladas de foto y termo período. Los valores de germinación se examinaron por análisis de variancia y test de significancia de Tukey. La germinación fue superior en cariopses pesados. El porcentaje de germinación de cariopses (livianos y pesados) fue superior al de antecios. Ninguno de los tratamientos considerados modificó la germinación de antecios y cariopses. El desarrollo foliar y radicular de las plántulas fue afectado por la aplicación de reguladores de crecimiento

Gravito-electromagnetic analogies

We reexamine and further develop different gravito-electromagnetic (GEM) analogies found in the literature, and clarify the connection between them. Special emphasis is placed in two exact physical analogies: the analogy based on inertial fields from the so-called "1+3 formalism", and the analogy based on tidal tensors. Both are reformulated, extended and generalized. We write in both formalisms the Maxwell and the full exact Einstein field equations with sources, plus the algebraic Bianchi identities, which are cast as the source-free equations for the gravitational field. New results within each approach are unveiled. The well known analogy between linearized gravity and electromagnetism in Lorentz frames is obtained as a limiting case of the exact ones. The formal analogies between the Maxwell and Weyl tensors are also discussed, and, together with insight from the other approaches, used to physically interpret gravitational radiation. The precise conditions under which a similarity between gravity and electromagnetism occurs are discussed, and we conclude by summarizing the main outcome of each approach.Comment: 60 pages, 2 figures. Improved version (compared to v2) with some re-write, notation improvements and a new figure that match the published version; expanded compared to the published version to include Secs. 2.3 and

Far Ultraviolet Spectroscopic Explorer Spectroscopy of the O VI Resonance Doublet in Sand 2 (WO)

We present Far Ultraviolet Spectroscopic Explorer spectroscopy of Sand 2, an LMC WO-type Wolf-Rayet star, revealing the O VI resonance P Cygni doublet at 1032-1038 Å. These data are combined with Hubble Space Telescope Faint Object Spectrograph ultraviolet and Mount Stromlo 2.3 m optical spectroscopy and analyzed using a spherical, non-LTE, line-blanketed code. Our study reveals exceptional stellar parameters: T* ~ 150,000 K, v∞ = 4100 km s-1, log(L/L☉) = 5.3, andimg1.gif = 1 × 10-5 M☉ yr-1, if we adopt a volume filling factor of 10%. Elemental abundances of C/He ~ 0.7 ± 0.2 and O/He ~ 0.15img2.gif by number qualitatively support previous recombination line studies. We confirm that Sand 2 is more chemically enriched in carbon than LMC WC stars and that it is expected to undergo a supernova explosion within the next 5 × 104 yr

Climatic zone and soil properties determine the biodiversity of the soil bacterial communities associated to native plants from desert areas of north-central algeria

Algeria is the largest country in Africa characterized by semi-arid and arid sites, located in the North, and hypersaline zones in the center and South of the country. Several autochthonous plants are well known as medicinal plants, having in common tolerance to aridity, drought and salinity. In their natural environment, they live with a great amount of microbial species that altogether are indicated as plant microbiota, while the plants are now viewed as a \u201cholobiont\u201d. In this work, the microbiota of the soil associated to the roots of fourteen economically relevant autochthonous plants from Algeria have been characterized by an innovative metagenomic approach with a dual purpose: (i) to deepen the knowledge of the arid and semi-arid environment and (ii) to characterize the composition of bacterial communities associated with indigenous plants with a strong economic/commercial interest, in order to make possible the improvement of their cultivation. The results presented in this work highlighted specific signatures which are mainly determined by climatic zone and soil properties more than by the plant species