169 research outputs found

    On the age of the magnetically active WW Psa and TX Psa members of the beta Pictoris association

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    There are a variety of different techniques available to estimate the ages of pre-main-sequence stars. Components of physical pairs, thanks to their strict coevality and the mass difference, such as the binary system analysed in this paper, are best suited to test the effectiveness of these different techniques. We consider the system WW Psa + TX Psa whose membership of the 25-Myr beta Pictoris association has been well established by earlier works. We investigate which age dating technique provides the best agreement between the age of the system and that of the association. We have photometrically monitored WW Psa and TX Psa and measured their rotation periods as P = 2.37d and P = 1.086d, respectively. We have retrieved from the literature their Li equivalent widths and measured their effective temperatures and luminosities. We investigate whether the ages of these stars derived using three independent techniques are consistent with the age of the beta Pictoris association. We find that the rotation periods and the Li contents of both stars are consistent with the distribution of other bona fide members of the cluster. On the contrary, the isochronal fitting provides similar ages for both stars, but a factor of about four younger than the quoted age of the association, or about 30% younger when the effects of magnetic fields are included. We explore the origin of the discrepant age inferred from isochronal fitting, including the possibilities that either the two components may be unresolved binaries or that the basic stellar parameters of both components are altered by enhanced magnetic activity. The latter is found to be the more reasonable cause, suggesting that age estimates based on the Li content is more reliable than isochronal fitting for pre-main-sequence stars with pronounced magnetic activity.Comment: Accepted by Astronomy and Astrophysics on December 13, 2016. 13 pages and 11 figure

    Testing Metal-poor Stellar Models and Isochrones with HST Parallaxes of Metal-poor Stars

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    Hubble Space Telescope (HST) fine guidance sensor observations were used to obtain parallaxes of eight metal-poor ([Fe/H] \u3c −1.4) stars. The parallaxes of these stars determined by the new Hipparcos reduction average 17% accuracy, in contrast to our new HST parallaxes, which average 1% accuracy and have errors on the individual parallaxes ranging from 85 to 144 μas. These parallax data were combined with HST Advanced Camera for Surveys photometry in the F606W and F814W filters to obtain the absolute magnitudes of the stars with an accuracy of 0.02–0.03 mag. Six of these stars are on the main sequence (MS) (with −2.7 \u3c [Fe/H] \u3c −1.8) and are suitable for testing metal-poor stellar evolution models and determining the distances to metal-poor globular clusters (GCs). Using the abundances obtained by O\u27Malley et al., we find that standard stellar models using the VandenBerg & Clem color transformation do a reasonable job of matching five of the MS stars, with HD 54639 ([Fe/H] = −2.5) being anomalous in its location in the color–magnitude diagram. Stellar models and isochrones were generated using a Monte Carlo analysis to take into account uncertainties in the models. Isochrones that fit the parallax stars were used to determine the distances and ages of nine GCs (with −2.4 ≤ [Fe/H] ≤ −1.9). Averaging together the age of all nine clusters led to an absolute age of the oldest, most metal-poor GCs of 12.7 ± 1.0 Gyr, where the quoted uncertainty takes into account the known uncertainties in the stellar models and isochrones, along with the uncertainty in the distance and reddening of the clusters

    Ações de capacitação no Assentamento 72, Ladário-MS, com enfoque na transição agroecológica.

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    Este trabalho é parte integrante das experiências de desenvolvimento local do projeto ?Alternativas para o desenvolvimento territorial rural do Assentamento 72 em Ladário MS, no Pantanal sul-mato-grossense, tendo como princípios básicos a agroecologia. O objetivo foi relatar as experiências decorrentes do projeto, visando à capacitação dos assentados para uma produção agroecológica. A metodologia esteve baseada na pesquisa ação e nos trabalhos de campo. O projeto começou a produzir transformações na organização social dos camponeses. This work is part of the experiences of local development project "Alternatives for the development of rural territory settlement 72 in Ladario-MS", in the Pantanalsul-mato-grossense, with the basic principles of agroecology. The objective was to report experiences from the project, used to teach the settlers for ecological production.The methodology was based on action research and field work. The project began producing transformations in the social organization of the peasantry.Também em: SEMINÁRIO DE AGROECOLOGIA DE MATO GROSSO DO SUL, 4.; ENCONTRO DE PRODUTORES AGROECOLÓGICOS DE MS, 3., 2012, Glória de Dourados. O saber tradicional e o científico: a interação encurtando caminhos para o desenvolvimento sustentável: anais. Brasília, DF: Embrapa, 2012. 1 CD-ROM. Editado por: Leandro Fávio Carneiro, Milton Parron Padovan

    Etnovariedades de mandioca (Manihot esculenta Crantz) cultivadas em assentamentos rurais de Corumbá, MS.

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    bitstream/CPAP/56599/1/BP78.pdfFormato Eletrônico

    Etnovariedades de mandioca (Manihot esculenta Crantz) cultivadas em assentamentos rurais de Corumbá, MS.

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    bitstream/CPATC-2009-09/20206/1/BP78.pd

    Feno da parte aérea da mandioca para a produção de ruminantes em sistemas organicos.

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    As produtividades de feno observadas neste estudo indicam que o aproveitamento da parte aérea da mandioca pode representar uma estratégia de integração das atividades produtivas em uma mesma propriedade apropriada para a alimentação de ruminantes durante o período de escassez das pastagens, constituindo em um recurso disponível para manter índices adequados de produtividade dos rebanhos da região manejados de acordo com as diretrizes da produção orgânica.bitstream/CPAP-2010/57326/1/CT88.pd

    Magnetic inflation and Stellar Mass. II. On the radii of wingle, rapidly rotating, fully convective M-dwarf stars

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    Main-sequence, fully convective M dwarfs in eclipsing binaries are observed to be larger than stellar evolutionary models predict by as much as 10%–15%. A proposed explanation for this discrepancy involves effects from strong magnetic fields, induced by rapid rotation via the dynamo process. Although, a handful of single, slowly rotating M dwarfs with radius measurements from interferometry also appear to be larger than models predict, suggesting that rotation or binarity specifically may not be the sole cause of the discrepancy. We test whether single, rapidly rotating, fully convective stars are also larger than expected by measuring their RsiniR\sin i distribution. We combine photometric rotation periods from the literature with rotational broadening (vsiniv\sin i) measurements reported in this work for a sample of 88 rapidly rotating M dwarf stars. Using a Bayesian framework, we find that stellar evolutionary models underestimate the radii by 10 \% \mbox{--}15{ \% }_{-2.5}^{+3}, but that at higher masses (0.18 < M < 0.4 M Sun), the discrepancy is only about 6% and comparable to results from interferometry and eclipsing binaries. At the lowest masses (0.08 < M < 0.18 M Sun), we find that the discrepancy between observations and theory is 13%–18%, and we argue that the discrepancy is unlikely to be due to effects from age. Furthermore, we find no statistically significant radius discrepancy between our sample and the handful of M dwarfs with interferometric radii. We conclude that neither rotation nor binarity are responsible for the inflated radii of fully convective M dwarfs, and that all fully convective M dwarfs are larger than models predict.The authors would like to thank the referee for the thoughtful report, which greatly improved the manuscript. The authors would also like to thank Lisa Prato and Larissa Nofi for IGRINS training, and Heidi Larson, Jason Sanborn, and Andrew Hayslip for operating the DCT during our observations. We would also like to thank Jen Winters, Jonathan Irwin, Paul Dalba, Mark Veyette, Eunkyu Han, and Andrew Vanderburg for useful discussions and helpful comments on this work. Some of this work was supported by the NASA Exoplanet Research Program (XRP) under grant No. NNX15AG08G issued through the Science Mission Directorate.These results made use of the Lowell Observatory's Discovery Channel Telescope, supported by Discovery Communications, Inc., Boston University, the University of Maryland, the University of Toledo and Northern Arizona University; the Immersion Grating Infrared Spectrograph (IGRINS) that was developed under a collaboration between the University of Texas at Austin and the Korea Astronomy and Space Science Institute (KASI) with the financial support of the US National Science Foundation under grant AST-1229522, of the University of Texas at Austin, and of the Korean GMT Project of KASI; data taken at The McDonald Observatory of The University of Texas at Austin; and data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by NASA and the NSF. (NNX15AG08G - NASA Exoplanet Research Program (XRP); Discovery Communications, Inc.; Boston University; University of Maryland; University of Toledo; Northern Arizona University; AST-1229522 - US National Science Foundation; University of Texas at Austin; Korean GMT Project of KASI; NASA; NSF
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