Crossing the Gould Belt in the Orion vicinity

We present a study of the large-scale spatial distribution of 6482 RASS X-ray sources in approximately 5000 deg^2 in the direction of Orion. We examine the astrophysical properties of a sub-sample of ~100 optical counterparts, using optical spectroscopy. This sub-sample is used to investigate the space density of the RASS young star candidates by comparing X-ray number counts with Galactic model predictions. We characterize the observed sub-sample in terms of spectral type, lithium content, radial and rotational velocities, as well as iron abundance. A population synthesis model is then applied to analyze the stellar content of the RASS in the studied area. We find that stars associated with the Orion star-forming region do show a high lithium content. A population of late-type stars with lithium equivalent widths larger than Pleiades stars of the same spectral type (hence younger than ~70-100 Myr) is found widely spread over the studied area. Two new young stellar aggregates, namely "X-ray Clump 0534+22" (age~2-10 Myr) and "X-ray Clump 0430-08" (age~2-20 Myr), are also identified. The spectroscopic follow-up and comparison with Galactic model predictions reveal that the X-ray selected stellar population in the direction of Orion is characterized by three distinct components, namely the clustered, the young dispersed, and the widespread field populations. The clustered population is mainly associated with regions of recent or ongoing star formation and correlates spatially with molecular clouds. The dispersed young population follows a broad lane apparently coinciding spatially with the Gould Belt, while the widespread population consists primarily of active field stars older than 100 Myr. We expect the "bi-dimensional" picture emerging from this study to grow in depth as soon as the distance and the kinematics of the studied sources will become available from the future Gaia mission.Comment: 17 pages, 13 figures, 4 tables. Accepted for publication in Astronomy and Astrophysics. Abstract shortene

Adsorción-desorción de los metales pesados Pb(II) y Hg(II) por modelos de partículas coloidales del suelo

4 páginas, 2 figuras, 1 tabla, 3 referencias.-- Publicado en el Capítulo IV: Contaminación y Medio Ambiente.-- Trabajo presentado a la XVII Reunión Científica de la Sociedad Española de Arcillas, celebrada en Elche (Alicante) y Castellón, del 27-29 de noviembre de 2002.El destino de los metales pesados en el medio ambiente está controlado por las reacciones de adsorción a los coloides del suelo. Por otro lado, las interacciones entre los constituyentes del suelo pueden alterar significativamente la cantidad y naturaleza de la superficie expuesta por los coloides del suelo para la adsorción de contaminantes. Por tanto, las predicciones sobre la extensión de la adsorción basadas en la suma de las capacidades adsorbentes de los constituyentes individuales del suelo pueden desviarse de lo que ocurre en la naturaleza (1). En la bibliografia han sido poco estudiadas las interacciones entre contaminantes y adsorbentes polifásicos, aunque en la última década ha aumentado la atención dada al estudio del comportamiento de modelos de asociaciones coloidales para obtener una interpretación más realista del proceso de adsorción en el suelo (2). En este trabajo se han determinado las capacidades adsorbentes de modelos de partículas coloidales binarias y ternarias que contienen montmorillonita (SW), ferrihidrita (Fh) y ácido húmico (AH) para dos contaminantes inorgánicos, los metales pesados Pb(lI) y Hg(II), Y se compararon con las capacidades de adsorción de los constituyentes individuales. Las partículas modelos se prepararon en el laboratorio y se caracterizaron por análisis elemental, espectroscopía infrarroja, difracción de rayos X y medidas de superficie específica. Se estudió la adsorción-desorción de Pb(lI) y Hg(ll) por parte de los diferentes adsorbentes y se utilizaron las técnicas de espectroscopía infrarroja y difracción de rayos X para analizar los mecanismos de interacción.Este trabajo ha sido financiado por el proyecto del MCYT REN2001-1700-C02- 01/TECNO y por el grupo RNM124 del PAI de la Junta de AndalucíaPeer reviewe

Córdoba taurina : apuntes biográficos de matadores, banderilleros, picadores, puntilleros, maletas, ganaderos, propietarios de plazas, empresarios, aficionados, revisteros y escritores taurinos antig..uos y modernos

Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2011Del texto se deduce impreso con posterioridad a 189

Hunting for brown dwarf binaries and testing atmospheric models with X-Shooter

The determination of the brown dwarf binary fraction may contribute to the understanding of the substellar formation mechanisms. Unresolved brown dwarf binaries may be revealed through their peculiar spectra or the discrepancy between optical and near-infrared spectral type classification. We obtained medium-resolution spectra of 22 brown dwarfs with these characteristics using the X-Shooter spectrograph at the VLT. We aimed to identify brown dwarf binary candidates, and to test if the BT-Settl 2014 atmospheric models reproduce their observed spectra. To find binaries spanning the L-T boundary, we used spectral indices and compared the spectra of the selected candidates to single spectra and synthetic binary spectra. We used synthetic binary spectra with components of same spectral type to determine as well the sensitivity of the method to this class of binaries. We identified three candidates to be combination of L plus T brown dwarfs. We are not able to identify binaries with components of similar spectral type. In our sample, we measured minimum binary fraction of $9.1^{+9.9}_{-3.0}$. From the best fit of the BT-Settl models 2014 to the observed spectra, we derived the atmospheric parameters for the single objects. The BT-Settl models were able to reproduce the majority of the SEDs from our objects, and the variation of the equivalent width of the RbI (794.8 nm) and CsI (852.0 nm) lines with the spectral type. Nonetheless, these models did not reproduce the evolution of the equivalent widths of the NaI (818.3 nm and 819.5 nm) and KI (1253 nm) lines with the spectral type.Comment: Accepted for publication in MNRA

The Spitzer c2d survey of large, nearby, interstellar clouds. X. The Chamaeleon II pre-main-sequence population as observed with IRAC and MIPS

We discuss the results from the combined IRAC and MIPS c2d Spitzer Legacy survey observations and complementary optical and NIR data of the Chamaeleon II (Cha II) dark cloud. We perform a census of the young population in an area of similar to 1.75 deg^(2) and study the spatial distribution and properties of the cloud members and candidate pre-main-sequence (PMS) objects and their circumstellar matter. Our census is complete down to the substellar regime (M approximate to 0.03 M☉). From the analysis of the volume density of the PMS objects and candidates we find two groups of objects with volume densities higher than 25 M☉ pc^(-3) and 5-10 members each. A multiplicity fraction of about 13% +/- 3% is observed for objects with separations 0.8" < θ < 6.0" (142-1065 AU). No evidence for variability between the two epochs of the c2d IRAC data set, Δt ~ 6 hr, is detected. We estimate a star formation efficiency of 1%-4%, consistent with the estimates for Taurus and Lupus, but lower than for Cha I. This might mean that different star formation activities in the Chamaeleon clouds reflect a different history of star formation. We also find that Cha II is turning some 6-7 M☉ into stars every Myr, which is low in comparison with the star formation rate in other c2d clouds. The disk fraction of 70%-80% that we estimate in Cha II is much higher than in other star-forming regions and indicates that the population in this cloud is dominated by objects with active accretion. Finally, the Cha II outflows are discussed; a new Herbig-Haro outflow, HH 939, driven by the classical T Tauri star Sz 50, has been discovered

A comprehensive CCD photometric study of the open cluster NGC 2421

We present the $UBVRI$ CCD photometry in the region of the open cluster NGC 2421. Radius of the cluster is determined as $\sim$ 3$^\prime$.0 using stellar density profile. Our Study indicates that metallicity of the cluster is $Z \sim$ 0.004. The reddening $E(B-V) = 0.42\pm$0.05 mag is determined using two colour $(U-B)$ versus $(B-V)$ diagram. By combining the 2MASS $JHK$ data with the optical data we determined $E(J-K) = 0.20\pm$0.20 mag and $E(V-K) = 1.15\pm$0.20 mag for this cluster. Colour-excess diagrams show normal interstellar extinction law in the direction of the cluster. We determined the distance of the cluster as 2.2$\pm$0.2 Kpc by comparing the ZAMS with the intrinsic CM diagram of the cluster. The age of the cluster has been estimated as 80$\pm$20 Myr using the stellar isochrones of metallicity $Z = 0.004$. The mass function slope $x = 1.2\pm0.3$ has been derived by applying the corrections of field stars contamination and data incompleteness. Our analysis indicate that the cluster NGC 2421 is dynamically relaxed.Comment: 10 pages, 13 figures, Accepted for publication in MNRA

Problems in the introduction of information in DAD-IS via internet

Only six coordinator of the countries enclosed in the European Regional Focal Point introduced the new information in DAD-IS via Internet, at least until the last workshop of the Point celebrated in Viena in summer of 1997. One of these countries was Spain and here we develop a brief description of the problems found in this activity.Los coordinadores de sólo seis países del Punto Focal Europeo introducen la nueva información en DAD-IS vía internet, al menos hasta la última reunión del punto celebrada en Viena en el verano de 1997. Uno de esos puntos fue España y aquí realizamos una breve descripción de la problemática encontrada en esta labor