The nearest young moving groups

The latest results in the research of forming planetary systems have led several authors to compile a sample of candidates for searching for planets in the vicinity of the sun. Young stellar associations are indeed excellent laboratories for this study, but some of them are not close enough to allow the detection of planets through adaptive optics techniques. However, the existence of very close young moving groups can solve this problem. Here we have compiled the members of the nearest young moving groups, as well as a list of new candidates from our catalogue of late-type stars possible members of young stellar kinematic groups, studying their membership through spectroscopic and photometric criteria.Comment: Latex file with 16 pages, 4 figures. Available at http://www.ucm.es/info/Astrof/invest/actividad/skg/skg_sag.html Accepted for publication in: The Astrophysical Journal (ApJ

Regulación y función de las brain-specific kinases 1 y 2 (BRSk1 y BRSk2, también llamadas SAD quinasas) en la diferenciación y sinapsis neuronales

Las proteínas quinasas BRSK1 y BRSK2 (Brain-specific kinase 1 y 2) pertenecen a la familia de las AMPK-related kinases, y son activadas mediante fosforilación por la proteína kinasa supresora de tumores LKB1. Las BRSKs se expresan mayoritariamente en cerebro, donde juegan un papel clave en el establecimiento de la polaridad neuronal y sinaptogénesis. En la neurona madura, BRSK1 modularía la función sináptica controlando la liberación de neurotransmisores en la neurona madura. Así pues, LKB1-BRSK1/2 constituye una nueva vía de señalización crucial para la función neuronal. Sin embargo, se desconoce cómo las BRSKs ejercen su función, dado que no se han descrito los mecanismos que regulan su actividad (LKB1 es una quinasa constitutivamente activa) ni los sustratos a través de los cuales median su función. En este trabajo se han obtenido y puesto a punto las herramientas bioquímicas para el estudio de las BRSKs (anticuerpos, constructos de DNA, preparaciones puras y activas, etc.), que se han utilizado para mostrar que tanto el desarrollo ontogénico del cerebro como la diferenciación neuronal transcurren con un aumento de expresión de BRSK1 y BRSK2. Mediante ensayos de gene-reporter luciferase e inmunoblots demostramos que las neurotrofinas NGF y BNDF promueven el aumento de la transcripción y expresión de las BRSKs, en un proceso mediado por la vía de señalización de Ras-Raf-MEK1-ERK1/2 y el factor de transcripción Sp1. Por otra parte, se ha caracterizado el patrón de localización subcelular de las BRSKs en neuronas corticales maduras: BRSK1 presenta un marcaje puntuado (similar al que del marcador de vesículas sinápticas sinaptofisina), y BRSK2 presenta una distribución homogénea a lo largo del soma, axón y dendritas, donde co-localiza con el marcador MAP2. Por primera vez se describe que las BRSKs se expresan en células gliales. Por primera vez se muestra en sinaptosomas de cerebro de rata la existencia de un pool de BRSK1, pero de BRSK2 o LKB1, en microdominios de membrana ricos en colesterol lipid rafts, y que esta localización resulta en una BRSK1 que presenta una mayor actividad kinasa que la proteína citosólica. Mediante ensayos de purificación de los lípidos de lipid rafts y reconstitución de vesículas multilamelares lipídicas, así como utilizando lípidos sintéticos, se muestra que la actividad kinasa BRSK1 (pero BRSK2) es regulada por el entorno lipídico mediante un mecanismo nuevo, diferente al de fosforilación por LKB1. Por último, se ha identificado un nuevo sustrato para BRSK1: la proteína t-SNARE sintaxina-1A, que regula la liberación de neurotransmisores a nivel presináptico. Mediante ensayos de fosforilación, generación de mutantes de deleción y análisis por espectrometría de masas se ha identificado un residuo de Serina como el residuo de sintaxina-1A fosforilado por BRSK1. Esta fosforilación presenta una estequiometría de 1 mol de fosfato incorporado por mol de sintaxina, y ha sido confirmada mediante ensayos radiométricos de fosforilación utilizando diferentes formas mutantes de las proteínas BRSK1 y sintaxina. Se ha generado y caracterizado un anticuerpo que reconoce específicamente el residuo de Ser fosforilado, lo que ha permitido demostrar que BRSK1 fosforila a esta Ser en sistemas celulares.Brain-specific kinase 1 and 2 (BRSK1 and BRSK2) belong to the AMPK-related family protein kinases, and they are activated by direct phosphorylation by the LKB1 tumor suppressor protein. BRSK proteins are expressed within the brain, where they play a crucial role for establishing neuronal polarity and synaptogenesis. BRSK1 also modulate synaptic function and neurotransmitter release in the mature neuron. Therefore, LKB1-BRSKs is a new signaling pathway that plays a pivotal role in neuronal function. However, how BRSKs exert their functions is unknown, since their substrates and the mechanisms modulating their activity remain to be described. In this study we have obtained new molecular and biochemical tools for the study of the BRSKs (antibodies, DNA constructs, etc), that allow us to show that neuronal differentiation and brain maturation processes take place with an increase of expression of BRSK1 and BRSK2 proteins. Using gene-reporter and immunoblot assays, we show that NGF and BDNF neurotrophins induce an increase on BRSKs transcription and translation, by a process which involves Ras-Raf-MEK1-ERK1/2 signaling pathway and the Sp1 transcription factor. We also study BRSKs subcellular localization from rat cultured cortical neurons by immunocytochemical assays. BRSK1 shows a punctuate pattern, similar to that observed for the synaptic vesicle protein marker synaptophysin, whereas BRSK2 mainly localize throughout the neuron in both axon and dendrites co-localizes with dendritic marker MAP2. We also report by the first time that glial cells express both, BRSK1 and BRSK2 proteins. We provide biochemical and pharmacological evidences demonstrating that a pool of BRSK1, but not BRSK2 or LKB1, localizes at membrane lipid rafts. We also show that raft-associated BRSK1 has higher activity than BRSK1 from non-raft environment. Further, recombinant BRSK1 activity increased 3-fold when assayed with small multilamellar vesicles (SMV) generated with both, lipids extracted from synaptosomal raft fractions or synthetic SMV made with authentic phosphatidylcholine, cholesterol and sphingomyelin. Interaction with lipid rafts represents a new mechanism of BRSK1 activity modulation, additional to T-loop phosphorylation. Finally, we have identified a new BRSK1 substrate, namely syntaxin-1A. Using phosphorylation and mass-spec analysis we have mapped and identified a residue of Ser that is mainly phosphorylated by BRSK1, showing a stechiometry of 1 mol P per mol of protein. We have generated an antibody that specifically recognizes this Ser residue and provided evidences showing that this phosphorylation occurs in vivo

The Tilapia-Prawn Polyculture: Its Development in Mexico

Objective: Analyze the productive development performed by two aquatic species of recent introduction in our country, the giant freshwater prawn (Macrobrachium rosenbergii) and tilapia (Oreochromis niloticus), arguing their potential under mono and polyculture systems. Design/methodology/approximation: The bibliographic meta-analysis was developed searching information on the internet, and is presented in a chronological manner with the analysis of the technological, social and political dimensions, visualizing the benefits and advantages of applying the polyculture production system. Results: A data base on the development of the tilapia-freshwater prawn polyculture in our country was obtained. Mexico presents the required physical characteristics for both species production. Thus, polyculture allows the use of the same infrastructure, resulting in a better productivity and income. Limitations of the study/implications: Polyculture information registered on electronic media was scarce. Findings/conclusions: The polyculture production of the Malaysian prawn and tilapia is a profitable option for the aquaculture producer in tropical areas of Mexico.Objective: Analyze the productive development performed by two aquatic species of recent introduction in our country, the giant freshwater prawn (Macrobrachium rosenbergii) and tilapia (Oreochromis niloticus), arguing their potential under mono and polyculture systems. Design/methodology/approximation: The bibliographic meta-analysis was developed searching information on the internet, and is presented in a chronological manner with the analysis of the technological, social and political dimensions, visualizing the benefits and advantages of applying the polyculture production system. Results: A data base on the development of the tilapia-freshwater prawn polyculture in our country was obtained. Mexico presents the required physical characteristics for both species production. Thus, polyculture allows the use of the same infrastructure, resulting in a better productivity and income. Limitations of the study/implications: Polyculture information registered on electronic media was scarce. Findings/conclusions: The polyculture production of the Malaysian prawn and tilapia is a profitable option for the aquaculture producer in tropical areas of Mexic

Chemically tagging the Hyades Supercluster: A homogeneous sample of F6-K4 kinematically selected northern stars

Stellar kinematic groups are kinematical coherent groups of stars that might have a common origin. These groups are dispersed throughout the Galaxy over time by the tidal effects of both Galactic rotation and disc heating, although their chemical content remains unchanged. The aim of chemical tagging is to establish that the abundances of every element in the analysis are homogeneus among the members. We study the case of the Hyades Supercluster to compile a reliable list of members (FGK stars) based on our chemical tagging analysis. For a total of 61 stars from the Hyades Supercluster, stellar atmospheric parameters (Teff, logg, xi, and [Fe/H]) are determined using our code called StePar, which is based on the sensitivity to the stellar atmospheric parameters of the iron EWs measured in the spectra. We derive the chemical abundances of 20 elements and find that their [X/Fe] ratios are consistent with Galactic abundance trends reported in previous studies. The chemical tagging method is applied with a carefully developed differential abundance analysis of each candidate member of the Hyades Supercluster, using a well-known member of the Hyades cluster as a reference (vB 153). We find that only 28 stars (26 dwarfs and 2 giants) are members, i.e. that 46% of our candidates are members based on the differential abundance analysis. This result confirms that the Hyades Supercluster cannot originate solely from the Hyades cluster.Comment: A&A, in pres

The field brown dwarf LP 944-20 and the Castor moving group

A reliable age estimation for the field brown dwarf LP 944-20 is accomplished through the analysis of its kinematic properties. The space velocities of this star strongly suggest its membership in the so-called Castor moving group. LP 944-20 can be sensibly assumed to have the group's age, which is estimated to be ~320 Myr, and metal content, which is found to be roughly solar. With these new constrains and the available photometry and lithium abundance, current brown dwarf models are put to a test. Using the IR magnitudes and the lithium diagnostics, the models are able to provide a reasonable description of the brown dwarf's properties (to within a few sigma) but yield an age which is roughly 50% larger than our estimate. Possible reasons for this discrepancy are discussed.Comment: 6 pages, 2 figures, accepted for publication in A&

Dynamical Masses of the Binary Brown Dwarf GJ 569Bab

We have obtained new images and high-resolution (R ~ 22400) near-infrared (1.2400-1.2575 micron) spectra of each component of the brown dwarf binary GJ 569Bab using the Adaptive Optics facility of the Keck II telescope and the NIRSPEC spectrometer. These data have allowed us to improve the determination of the astrometric orbit and to measure radial velocities of the components. We have used the astrometric and spectroscopic measurements to derive the dynamical mass of each brown dwarf and the systemic velocity of the pair by means of a chi^2 fitting technique. From various considerations, the mass of each component is likely in the range 0.034-0.070 Msol (GJ 569Bb) and 0.055-0.087 Msol (GJ 569Ba). This implies that the mass ratio, q, of the binary is greater than 0.4, being the most likely value q = 0.75-0.85. Adopting 0.072 Msol as the most conservative location of the substellar limit for solar metallicity, our analysis confirms GJ 569Bb as the first genuine brown dwarf known without any theoretical assumption. We have compared the dynamical masses of GJ 569Ba and Bb, and their effective temperatures and luminosities, to the predictions of state-of-the-art theoretical evolutionary isochrones, finding that models exhibit good performance in the regime of high substellar masses if the binary is about a few hundred million years old. However, the surface gravities of GJ 569Ba (M8.5V) and Bb (M9V) derived from our spectral analysis (the observed data have been compared to the latest synthetic spectra) appear to be smaller than the values provided by the evolutionary models.Comment: 36 pages (tables and figures included). Accepted for publication in Ap

The discovery of new warm debris disks around F-type stars

We report the discovery of four rare debris disks with warm excesses around F-stars, significantly increasing the number of such systems known in the solar neighborhood. Three of the disks are consistent with the predictions of steady state planetesimal disk evolution models. The oldest source, HD 169666, displays a dust fractional luminosity too high to be in steady state and we suggest that this system recently underwent a transient event of dust production. In addition, two spectra of this star separated by ~three years show silicate emission features, indicative of submicron- to micron-sized grains. We argue that such small grains would be rapidly depleted and their presence in both spectra suggests that the production of small dust is continuous over at least on few years timescale. We predict that systems showing variable mid-infrared spectra, if exist, will provide valuable help in distinguishing the possible scenarios proposed for dust replenishment.Comment: Accepted for publication in ApJ Letters, 13 pages, 2 figures, 2 table

Ages of A-type Vega-like stars from uvbyβ\beta Photometry

We have estimated the ages of a sample of A-type Vega-like stars by using Str\"{o}mgren \emph{uvby$\beta} photometric data and theoretical evolutionary tracks. We find that 13 percent of these A stars have been reported as Vega-like stars in the literature and that the ages of this subset run the gamut from very young (50~Myr) to old (1~Gyr), with no obvious age difference compared to those of field A stars. We clearly show that the fractional IR luminosity decreases with the ages of Vega-like stars.Comment: 4pages text, 3 tables, 3 figures, Accepted in Ap

Analysis of Peculiarities of the Stellar Velocity Field in the Solar Neighborhood

Based on a new version of the Hipparcos catalogue and an updated Geneva-Copenhagen survey of F and G dwarfs, we analyze the space velocity field of about 17000 single stars in the solar neighborhood. The main known clumps, streams, and branches (Pleiades, Hyades, Sirius, Coma Berenices, Hercules, Wolf 630-alpha Ceti, and Arcturus) have been identified using various approaches. The evolution of the space velocity field for F and G dwarfs has been traced as a function of the stellar age. We have managed to confirm the existence of the recently discovered KFR08 stream. We have found 19 Hipparcos stars, candidates for membership in the KFR08 stream, and obtained an isochrone age estimate for the stream, 13 Gyr. The mean stellar ages of the Wolf 630-alpha Ceti and Hercules streams are shown to be comparable, 4--6 Gyr. No significant differences in the metallicities of stars belonging to these streams have been found. This is an argument for the hypothesis that these streams owe their origin to a common mechanism.Comment: 23 pages, 9 figure

Kinematic Peculiarities of Gould Belt Stars

We analyzed the space velocities of Gould Belt stars younger than 125 Myr located at heliocentric distances <650 pc. We determined the rotation and expansion parameters of the Gould Belt by assuming the existence of a single kinematic center whose direction was found to be the following: $l_\circ=128^\circ$ and $R_\circ=150$ pc. The linear velocities reach their maximum at a distance of $\approx300$ pc from the center and are -6 km s$^{-1}$ for the rotation (whose direction coincides with the Galactic rotation) and +4 km s$^{-1}$ for the expansion. The stellar rotation model used here is shown to give a more faithful description of the observed velocity field than the linear model based on the Oort constants $A_G$ and $B_G$. We present evidence that the young clusters $\beta$ Pic, Tuc/HorA, and TWA belong to the Gould Belt structure.Comment: 17 pages, 5 figure