UVES spectra of young brown dwarfs in Cha I: radial and rotational velocities

Based on high-resolution UVES spectra we found that the radial velocity (RV) dispersion of nine of twelve known young bona fide and candidate brown dwarfs in the Cha I dark cloud is 2.0 km/s, i.e. significantly smaller than the RV dispersion of T Tauri stars in Cha I (3.6 km/s) and only slightly larger than the dispersion of the surrounding molecular gas (1.2 km/s) (Mizuno et al. 1999). This result indicates that the majority of these brown dwarfs are not ejected with high velocity out of a dense region as proposed by some formation scenarios for brown dwarfs. The mean RV values are consistent with the objects being kinematic members of Cha I. The RV dispersion of the T Tauri stars confined to the Cha I region is based on a compilation of T Tauri stars with known RVs from the literature plus three T Tauri stars observed with UVES and unpublished RVs for nine T Tauri stars. Time-resolved spectroscopy revealed RV variations for five out of nine of the bona fide and candidate brown dwarfs in Cha I, which could be due to orbiting planets or surface features. Furthermore we derived rotational velocities vsin(i) and the Lithium 6708 \AA equivalent width.Comment: A&A Letter, in pres

A proper motion study of the Lupus clouds using VO tools

Aims: By using kinematical information, we test the membership of the new Lupus candidate members proposed by the Cores to Disks (c2d) Spitzer Legacy Program program and by a complementary optical survey. We also investigate the relationship between the proper motions (pm) and other properties, in order to get some clues about their formation and early evolution. Methods: We compiled a list of members and possible members of Lupus 1, 3, and 4, together with all information on their spectral types, disks, and physical parameters. Using VO-tools, we cross-matched this list with the astrometric catalogues to get pm. Our final sample contains sources with magnitudes I<16mag and estimated masses >~0.1Msun. Results: According to the kinematic information, our sources can be divided into two main groups. The first one contains sources with higher pm in agreement with other Gould Belt populations and with spatial distribution, optical and near-infrared colours, and disk composition consistent with these objects belonging to the Lupus clouds. In the second group, sources have lower pm with random orientations, and they are mostly located outside the cloud cores, making their association with the Lupus complex more doubtful. We investigate the properties of the higher pm group, but cannot find any correlations with spatial location, binarity, the presence of a circumstellar disk, or with physical properties such as effective temperature, luminosity, mass, or age. Conclusions: We conclude that the lower pm group probably represents a background population or mixture of populations unrelated to the Lupus clouds. The higher pm group, on the other hand, has properties consistent with it being a genuine population of the Lupus star-forming region. More accurate pm and/or radial velocity information are required for a more detailed study of the kinematic properties of the Lupus stellar members.Comment: Accepted in A&

X-Shooter spectroscopy of young stellar objects: II. Impact of chromospheric emission on accretion rate estimates

Context. The lack of knowledge of photospheric parameters and the level of chromospheric activity in young low-mass pre-main sequence stars introduces uncertainties when measuring mass accretion rates in accreting (Class II) Young Stellar Objects. A detailed investigation of the effect of chromospheric emission on the estimates of mass accretion rate in young low-mass stars is still missing. This can be undertaken using samples of young diskless (Class III) K and M-type stars. Aims. Our goal is to measure the chromospheric activity of Class III pre main sequence stars to determine its effect on the estimates of accretion luminosity (Lacc) and mass accretion rate (Macc) in young stellar objects with disks. Methods. Using VLT/X-Shooter spectra we have analyzed a sample of 24 non-accreting young stellar objects of spectral type between K5 and M9.5. We identify the main emission lines normally used as tracers of accretion in Class II objects, and we determine their fluxes in order to estimate the contribution of the chromospheric activity to the line luminosity. Results. We have used the relationships between line luminosity and accretion luminosity derived in the literature for Class II objects to evaluate the impact of chromospheric activity on the accretion rate measurements. We find that the typical chromospheric activity would bias the derived accretion luminosity by Lacc,noise< 10-3Lsun, with a strong dependence with the Teff of the objects. The noise on Macc depends on stellar mass and age, and the typical values of log(Macc,noise) range between -9.2 to -11.6Msun/yr. Conclusions. Values of Lacc< 10-3Lsun obtained in accreting low-mass pre main sequence stars through line luminosity should be treated with caution as the line emission may be dominated by the contribution of chromospheric activity.Comment: accepted for publication in Astronomy & Astrophysic

X-Shooter spectroscopy of young stellar objects: IV -- Accretion in low-mass stars and sub-stellar objects in Lupus

We present X-Shooter/VLT observations of a sample of 36 accreting low-mass stellar and sub-stellar objects (YSOs) in the Lupus star forming region, spanning a range in mass from ~0.03 to ~1.2Msun, but mostly with 0.1Msun < Mstar < 0.5Msun. Our aim is twofold: firstly, analyse the relationship between excess-continuum and line emission accretion diagnostics, and, secondly, to investigate the accretion properties in terms of the physical properties of the central object. The accretion luminosity (Lacc), and from it the accretion rate (Macc), is derived by modelling the excess emission, from the UV to the near-IR, as the continuum emission of a slab of hydrogen. The flux and luminosity (Ll) of a large number of emission lines of H, He, CaII, etc., observed simultaneously in the range from ~330nm to 2500nm, were computed. The luminosity of all the lines is well correlated with Lacc. We provide empirical relationships between Lacc and the luminosity of 39 emission lines, which have a lower dispersion as compared to previous relationships in the literature. Our measurements extend the Pab and Brg relationships to Lacc values about two orders of magnitude lower than those reported in previous studies. We confirm that different methodologies to measure Lacc and Macc yield significantly different results: Ha line profile modelling may underestimate Macc by 0.6 to 0.8dex with respect to Macc derived from continuum-excess measures. Such differences may explain the likely spurious bi-modal relationships between Macc and other YSOs properties reported in the literature. We derive Macc in the range 2e-12 -- 4e-8 Msun/yr and conclude that Macc is proportional to Mstar^1.8(+/-0.2), with a dispersion lower by a factor of about 2 than in previous studies. A number of properties indicate that the physical conditions of the accreting gas are similar over more than 5 orders of magnitude in Macc

Evidence for the concurrent growth of thick discs and central mass concentrations from S 4 G imaging

We have produced 3.6 &mu;m + 4.5 &mu;m vertically integrated radial luminosity profiles of 69 edge-on galaxies from the Spitzer Survey of Stellar Structure in Galaxies (SG). We decomposed the luminosity profiles into a disc and a central mass concentration (CMC). These fits, combined with thin/thick disc decompositions from our previous studies, allow us to estimate the masses of the CMCs, the thick discs, and the thin discs (&alpha;, &alpha;, and &alpha;). We obtained atomic disc masses (&alpha;) from the literature. We then consider the CMC and the thick disc to be dynamically hot components and the thin disc and the gas disc to be dynamically cold components. We find that the ratio between the mass of the hot components and that of the cold components, (&alpha; + &alpha;)/(&alpha; + &alpha;), does not depend on the total galaxy mass as described by circular velocities (v). We also find that the higher the v, the more concentrated the hot component of a galaxy. We suggest that our results are compatible with having CMCs and thick discs built in a short and early high star forming intensity phase. These components were born thick because of the large scale height of the turbulent gas disc in which they originated. Our results indicate that the ratio between the star forming rate in the former phase and that of the formation of the thin disc is of the order of 10, but the value depends on the duration of the high star forming intensity phase.</p

X-Shooter spectroscopy of young stellar objects III. Photospheric and chromospheric properties of Class III objects

We analyzed X-Shooter/VLT spectra of 24 ClassIII sources from three nearby star-forming regions (sigmaOrionis, LupusIII, and TWHya). We determined the effective temperature, surface gravity, rotational velocity, and radial velocity by comparing the observed spectra with synthetic BT-Settl model spectra. We investigated in detail the emission lines emerging from the stellar chromospheres and combined these data with archival X-ray data to allow for a comparison between chromospheric and coronal emissions. Both X-ray and Halpha luminosity as measured in terms of the bolometric luminosity are independent of the effective temperature for early-M stars but decline toward the end of the spectral M sequence. For the saturated early-M stars the average emission level is almost one dex higher for X-rays than for Halpha: log(L_x/L_bol) = -2.85 +- 0.36 vs. log(L_Halpha/L_bol) = -3.72 +- 0.21. When all chromospheric emission lines (including the Balmer series up to H11, CaII HK, the CaII infrared triplet, and several HeI lines) are summed up the coronal flux still dominates that of the chromosphere, typically by a factor 2-5. Flux-flux relations between activity diagnostics that probe different atmospheric layers (from the lower chromosphere to the corona) separate our sample of active pre-main sequence stars from the bulk of field M dwarfs studied in the literature. Flux ratios between individual optical emission lines show a smooth dependence on the effective temperature. The Balmer decrements can roughly be reproduced by an NLTE radiative transfer model devised for another young star of similar age. Future, more complete chromospheric model grids can be tested against this data set.Comment: accepted for publication in Astronomy & Astrophysic

Direct and indirect use of water in a dairy system

La gestión de los recursos hídricos se ha convertido en un tema de suma importancia a nivel mundial. El objetivo del trabajo fue evaluar el uso del agua en un sistema de producción de leche Se evaluó el uso directo e indirecto del agua en un sistema de base pastoril (40%), con una carga de 2 VT/ha, contemplando el alimento importado al sistema versus el suministrado a los animales. El periodo evaluado fue desde junio de 2011 hasta julio de 2012. El agua directa es aquella usada en las tareas de higiene de la máquina de ordeño (MqO) y del equipo de frío (EF), en la placa de refrescado (PR) y como bebida animal. Los consumos de agua para la limpieza de la instalación de ordeño, corrales anexos y el agua de bebida se obtuvieron por caudalímetro y por fórmula para: MqO, litros/día (l/d)=27,75*número de unidades de ordeño+134,4 y EF, l/d=0,0403*capacidad tanque (l)+11,153. Para la PR se utilizó un valor promedio de 2,75 l agua/l leche a refrescar. El agua indirecta es la necesaria para producir los alimentos importados (balanceado, grano maíz, semilla algodón y pellet soja) y propios (pasturas y cultivos anuales en secano). Para su cálculo se utilizaron los programas CLIMWAT 2.0 y CROPWAT de la FAO, adaptando los ciclos de los cultivos con datos del sistema y regionales. En el Cuadro se observa que el consumo de agua total en el sistema considerando el alimento suministrado fue de 951,2 y con alimento importado fue 1.151,5 l/l (21,1% mayor). El consumo directo de agua solo representó menos del 1% de la cantidad total utilizada en el sistema, siendo el agua de bebida y la de PR las principales contribuyentes. El consumo indirecto representó más del 99%, compuesto mayoritariamente por el agua utilizada por las pasturas y por los alimentos importados. El análisis más detallado de esta fracción permitiría detectar las variables de mayor peso en el uso del agua, mejorando el manejo de este recurso en un sistema de producción lechero.Fil: Tieri, M. P.. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Santa Fe. Estación Experimental Agropecuaria, Rafaela; Argentina;Fil: Pece, Marta Graciela del Valle. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Santa Fe. Estación Experimental Agropecuaria, Rafaela; Argentina;Fil: Charlon, Veronica. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Santa Fe. Estación Experimental Agropecuaria, Rafaela; Argentina;Fil: Comerón, E.. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Santa Fe. Estación Experimental Agropecuaria, Rafaela; Argentina;Fil: Civit, Bárbara María. Universidad Tecnológica Nacional. Facultad Regional de Mendoza; Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - CONICET - Mendoza. Instituto de Ciencias Humanas, Sociales y Ambientales; Argentina

High Moisture Sorghum Grain Silage: Effects of Tannin Content and Urea Treatment on the Performance of Dairy Cows

Grain sorghum silage tannin content effect was evaluated on milk production and chemical composition of Argentinean Holstein bred cows, and it are described dry matter (DM) and crude protein (CP) in situ digestion parameters and effective degradability. The base diet was constituted by alfalfa pasture, maize silage, and a protein – mineral supplement, differing in three treatments based on high moisture grain silage characteristic: LTS= Low tannin grain sorghum, HTS= High tannin grain sorghum, and HTSu= High tannin sorghum plus the addition of urea. Grain sorghum silage tannin content affects milk production, without significant alteration of chemical composition. Beside the effect of urea addition on grain sorghum tannin content, improvement in animal response was only moderate

Detection of nonthermal emission from the bow shock of a massive runaway star

The environs of massive, early-type stars have been inspected in recent years in the search for sites where particles can be accelerated up to relativistic energies. Wind regions of massive binaries that collide have already been established as sources of high-energy emission; however, there is a different scenario for massive stars where strong shocks can also be produced: the bow-shaped region of matter piled up by the action of the stellar strong wind of a runaway star interacting with the interstellar medium. We study the bow-shock region produced by a very massive runaway star, BD+43 3654, to look for nonthermal radio emission as evidence of a relativistic particle population. We observed the field of BD+43 3654 at two frequencies, 1.42 and 4.86 GHz, with the Very Large Array (VLA), and obtained a spectral index map of the radio emission. We have detected, for the first time, nonthermal radio emission from the bow shock of a massive runaway star. After analyzing the radiative mechanisms that can be at work, we conclude that the region under study could produce enough relativistic particles whose radiation might be detectable by forthcoming gamma-ray instruments, like CTA North.Comment: Accepted in Astronomy and Astrophysics Letter