Is there a propeller neutron star in γ\gamma Cas?

$\gamma$ Cas is the prototype of a small population of B0-B1.5 III-V classical Be (cBe) stars that emit anomalous and hard X-rays with a unique array of properties. $\gamma$ Cas is known to host, like other cBe stars, a decretion disk and also a low mass companion. Recently Postnov et al. have posited that this companion is a magnetized rapidly spinning neutron star that deflects direct gravitational accretion from a stellar/disk wind via the "propeller mechanism." These authors state that the key X-ray observations are "remarkably well produced" in this scenario. We reexamine this mechanism in detail and conclude that there are a number of fatal objections in its application to the $\gamma$ Cas case. Among other considerations these issues include the prediction under the propeller scenario of a much smaller population of $\gamma$ Cas stars than is observed and the lack of allowance for observed correlations of X-ray and UV and/or optical properties over a variety of timescales.Comment: 9 page

Stellar parameters for stars of the CoRoT exoplanet field

Aims:To support the computation and evolutionary interpretation of periods associated with the rotational modulation, oscillations, and variability of stars located in the CoRoT fields, we are conducting a spectroscopic survey for stars located in the fields already observed by the satellite. These observations allow us to compute physical and chemical parameters for our stellar sample. Method: Using spectroscopic observations obtained with UVES/VLT and Hydra/Blanco, and based on standard analysis techniques, we computed physical and chemical parameters ($T_{\rm{eff}}$, $\log \,(g)$, $\rm{[Fe/H]}$, $v_{\rm{mic}}$, $v_{\rm{rad}}$, $v \sin \,(i)$, and $A(\rm{Li})$) for a large sample of CoRoT targets. Results: We provide physical and chemical parameters for a sample comprised of 138 CoRoT targets. Our analysis shows the stars in our sample are located in different evolutionary stages, ranging from the main sequence to the red giant branch, and range in spectral type from F to K. The physical and chemical properties for the stellar sample are in agreement with typical values reported for FGK stars. However, we report three stars presenting abnormal lithium behavior in the CoRoT fields. These parameters allow us to properly characterize the intrinsic properties of the stars in these fields. Our results reveal important differences in the distributions of metallicity, $T_{\rm eff}$, and evolutionary status for stars belonging to different CoRoT fields, in agreement with results obtained independently from ground-based photometric surveys. Conclusions: Our spectroscopic catalog, by providing much-needed spectroscopic information for a large sample of CoRoT targets, will be of key importance for the successful accomplishment of several different programs related to the CoRoT mission, thus it will help further boost the scientific return associated with this space mission.Comment: 43 pages, 17 figures, accepted for publication in A&

The WFCAM Multi-wavelength Variable Star Catalog

Stellar variability in the near-infrared (NIR) remains largely unexplored. The exploitation of public science archives with data-mining methods offers a perspective for the time-domain exploration of the NIR sky. We perform a comprehensive search for stellar variability using the optical-NIR multi-band photometric data in the public Calibration Database of the WFCAM Science Archive (WSA), with the aim of contributing to the general census of variable stars, and to extend the current scarce inventory of accurate NIR light curves for a number of variable star classes. We introduce new variability indices designed for multi-band data with correlated sampling, and apply them for pre-selecting variable star candidates, i.e., light curves that are dominated by correlated variations, from noise-dominated ones. Pre-selection criteria are established by robust numerical tests for evaluating the response of variability indices to colored noise characteristic to the data. We find 275 periodic variable stars and an additional 44 objects with suspected variability with uncertain periods or apparently aperiodic variation. Only 44 of these objects had been previously known, including 11 RR~Lyrae stars in the outskirts of the globular cluster M3 (NGC~5272). We provide a preliminary classification of the new variable stars that have well-measured light curves, but the variability types of a large number of objects remain ambiguous. We classify most of the new variables as contact binary stars, but we also find several pulsating stars, among which 34 are probably new field RR~Lyrae and 3 are likely Cepheids. We also identify 32 highly reddened variable objects close to previously known dark nebulae, suggesting that these are embedded young stellar objects. We publish our results and all light-curve data as the WFCAM Variable Star Catalog.Comment: 21 pages, 11 figure

Possibilidades da produção integrada em hortaliças.

Edição de Resumos expandidos e palestras do 43 Congresso Brasileiro de Olericultura, Recife, jul. 2003

The Digitized Second Palomar Observatory Sky Survey (DPOSS) II: Photometric Calibration

We present the photometric calibration technique for the Digitized Second Palomar Observatory Sky Survey (DPOSS), used to create seamless catalogs of calibrated objects over large sky areas. After applying a correction for telescope vignetting, the extensive plate overlap regions are used to transform sets of plates onto a common instrumental photometric system. Photometric transformations to the Gunn gri system for each plate, for stars and galaxies, are derived using these contiguous stitched areas and an extensive CCD imaging library obtained for this purpose. We discuss the resulting photometric accuracy, survey depth, and possible systematic errors.Comment: 25 pages, 13 figures. Accepted to AJ. Some figures shrunk or missing to limit file size; the full paper is available at http://www.sdss.jhu.edu/~rrg/science/papers/photometrypaper.ps.g

Caracterização física e físico-química dos frutos da cajazeira (Spondias mombin L.) e de suas polpas obtidas por dois tipos de extrator.

O cajá é um fruto amplamente consumido in natura ou na forma de produtos processados nas regiões Norte e Nordeste do Brasil. Devido à crescente aceitação de seus produtos e à busca por novos sabores, a agroindústria de sua polpa vem despertando interesse no mercado interno brasileiro e nas exportações. Entretanto, apesar do forte interesse comercial, poucos dados científicos sobre o fruto são encontrados. Assim, o objetivo desse trabalho foi caracterizar física e físico-quimicamente a polpa dos frutos provenientes de Belém-Pará, além de avaliar compostos relacionados à funcionalidade. Dessa forma, realizaram-se análises de composição centesimal, assim como determinação de pH, acidez titulável total, sólidos solúveis, açúcares totais e redutores, vitamina C, taninos e carotenoides totais, além da avaliação instrumental de cor. A pesquisa também se propôs a avaliar dois tipos de equipamentos (pás e escovas) para um estudo comparativo da extração mecânica da polpa. Análises microbiológicas foram realizadas, características físico-químicas novamente estudadas, assim como o rendimento e a quebra de sementes durante as extrações foram avaliados. Os resultados revelaram que o fruto em estudo apresentou dimensões variáveis, com peso entre 1,35 e 16,47 g, com valor médio de 7,19 g. Em relação às características físico-químicas, a polpa foi considerada ácida (pH de 2,53, acidez titulável de 1,86% e baixo teor de açúcares totais de 4,54 g.100 g-1) e se destacou quanto aos teores de taninos (299,81 mg.100 g-1) e carotenoides (28,30 µg.100 g-1). O tipo de extrator utilizado interferiu nestas características, sendo significativamente diferentes (Tukey a p ≤ 0,05). O extrator do tipo escovas apresentou maior rendimento em polpa (33,25%), maior teor de carotenoides totais (38,56 µg.g-1), menor quebra de sementes e, consequentemente, um menor teor em taninos (314,78 mg.100 g-1). Este mesmo extrator, quando comparado ao extrator de pás, também apresentou as melhores condições de processo para o fruto e melhor qualidade microbiológica do produto final