Oxygen and silicon abundances in Cygnus OB2: Chemical homogeneity in a sample of OB slow rotators

Cygnus OB2 is a rich OB association in the Galaxy which has experienced intense star formation in the last 20-25 Myr. Its stellar population shows a correlation between age and Galactic longitude. Exploring the chemical composition of its stellar content we will be able to check the degree of homogeneity of the natal molecular cloud and possible effects of self-enrichment processes. Our aim is to determine silicon and oxygen abundances for a sample of eight early-type slow rotators in Cygnus OB2 in order to check possible inhomogeneities across the whole association and whether there exists a correlation of chemical composition with Galactic longitude. We have performed a spectroscopic analysis of a sample of late O and early B stars with low rotational velocity, which have been chosen so as to cover the whole association area. We have carried out an analysis based on equivalent widths of metal lines, the wings of the H Balmer lines and FASTWIND stellar atmosphere models to determine their stellar fundamental parameters as well as the silicon and oxygen surface abundances. We derive a rather homogeneous distribution of silicon and oxygen abundances across the region, with average values of 12+log(Si/H)=7.53$\pm$0.08 dex and 12+log(O/H)=8.65$\pm$0.12 dex. We find a homogeneous chemical composition in Cygnus OB2 with no clear evidence for significant chemical self-enrichment, despite indications of strong stellar winds and possible supernovae during the history of the region. Comparison with different scenarios of chemical enrichment by stellar winds and supernovae point to star forming efficiencies not significantly above 10%. The degree of homogeneity that we find is consistent with the observed Milky Way oxygen gradient based on HII regions. We also find that the oxygen scatter within Cygnus OB2 is at least of the same order than among HII regions at similar Galactocentric distance.Comment: 15 pages, 7 figures, accepted for publication in Astronomy & Astrophysic

Accounting for Stochastic Fluctuations when Analysing Integrated Light of Star Clusters. I: First Systematics

Star clusters are studied widely both as benchmarks for stellar evolution models and in their own right. Cluster age and mass distributions within galaxies are probes of star formation histories, and of cluster formation and disruption processes. The vast majority of clusters in the Universe is small, and it is well known that the integrated fluxes and colors have broad probability distributions, due to small numbers of bright stars. This paper goes beyond the description of predicted probability distributions, and presents results of the analysis of cluster energy distributions in an explicitly stochastic context. The method developed is Bayesian. It provides posterior probability distributions in the age-mass-extinction space, using multi-wavelength photometric observations and a large collection of Monte-Carlo simulations of clusters of finite stellar masses. Both UBVI and UBVIK datasets are considered, and the study conducted in this paper is restricted to the solar metallicity. We first reassess and explain errors arising from the use of standard analysis methods, which are based on continuous population synthesis models: systematic errors on ages and random errors on masses are large, while systematic errors on masses tend to be smaller. The age-mass distributions obtained after analysis of a synthetic sample are very similar to those found for real galaxies in the literature. The Bayesian approach on the other hand, is very successful in recovering the input ages and masses. Taking stochastic effects into account is important, more important for instance than the choice of adding or removing near-IR data in many cases. We found no immediately obvious reason to reject priors inspired by previous (standard) analyses of cluster populations in galaxies, i.e. cluster distributions that scale with mass as M^-2 and are uniform on a logarithmic age scale.Comment: 17 pages, 13 figures, Accepted for publication in A&A

Los departamentos del oeste de la provincia de Catamarca y su anexión provisoria a la provincia de Tucumán : Diciembre 1835-noviembre 1838

Por decreto de 5 de diciembre de 1835, el gobernador Alejandro Heredia anexionó los departamentos de Santa Maria y Andalgalá a la provincia de Tucumán. En el artículo 1º se especifica que la medida obedece a que los citados departamentos "se han emancipado de la Capital de Catamarca y agregado a la de Tucumán, según consta de las solemnes actas celebradas por todas las autoridades, vecinos sensatos de dichos departamentos". Y en el art. 5º se dice que "a pesar de que el Gobierno de Tucumán se había substraído hasta aquí a la aceptación de la resolución indicada en el art. 1º hoy se ve precisado a tomar esta medida provisoria mientras dure el conflicto y apuro en que nuevamente han puesto a la provincia y república las insidiosas miras de los malvados".Departamento de Histori

Los departamentos del oeste de la provincia de Catamarca y su anexión provisoria a la provincia de Tucumán : Diciembre 1835-noviembre 1838

Por decreto de 5 de diciembre de 1835, el gobernador Alejandro Heredia anexionó los departamentos de Santa Maria y Andalgalá a la provincia de Tucumán. En el artículo 1º se especifica que la medida obedece a que los citados departamentos "se han emancipado de la Capital de Catamarca y agregado a la de Tucumán, según consta de las solemnes actas celebradas por todas las autoridades, vecinos sensatos de dichos departamentos". Y en el art. 5º se dice que "a pesar de que el Gobierno de Tucumán se había substraído hasta aquí a la aceptación de la resolución indicada en el art. 1º hoy se ve precisado a tomar esta medida provisoria mientras dure el conflicto y apuro en que nuevamente han puesto a la provincia y república las insidiosas miras de los malvados".Departamento de Histori

Synthesis models in a probabilistic framework: metrics of fitting

In general, synthesis models provide the mean value of the distribution of possible integrated luminosities, this distribution (and not only its mean value) being the actual description of the integrated luminosity. Therefore, to obtain the closest model to an observation only provides confi- dence about the precision of such a fit, but not information about the accuracy of the result. In this contribution we show how to overcome this drawback and we propose the use of the theoretical mean-averaged dispersion that can be produced by synthesis models as a metric of fitting to infer accurate physical parameters of observed systems.Comment: Invited talk in "New Quests in stellar astrophysics II. Ultraviolet properties of evolved stellar populations" in press. 8 pages, 5 figures. (Part II on metric of fitting for population synthesis

Subjective satisfaction in long-term orthokeratology patients

Purpose: To AU3 evaluate the subjective satisfaction in visual stability, night vision complains, and light distortion phenomena, and also the number of hours and days per week of lens wear, in patients with myopia undergoing orthokeratology (OK) treatment for at least 1 year. Methods: A visual analog scale (VAS) questionnaire containing 18 items was administered to 44 patients, 29 women and 15 men (mean age, 24.39 6 9.11 years), with a baseline spherical equivalent refractive error of 22.40 6 0.94 diopters and astigmatism up to 20.5 diopters. Average treatment period by the time of data collection was 19 6 7 months. Patients rated their satisfaction with the correction, with complaints of visual distortion being graded on a scale of 0 to 10, where 0 indicated no discomfort at all. Results: More than 50% of patients skipped lens wear at least 1 night per week. The most common wearing pattern was 6–8 hours a day for 72.7% with 54.5% of patients wearing lenses every 2–3 nights only. Subjective vision scores after lens removal was 9.1 6 1.1 after having worn the lenses and 8.1 6 1.4 after skipping lens wear for 1 night. Subjective vision scores before lens insertion at the end of the day was 6.9 6 2.0 and 5.8 6 2.4, respectively. The number of hours until noticeable blur reduced with increased level of baseline myopia (r = 0.396; P , 0.001). Conclusion: Orthokeratology patients show an irregular wearing pattern after 1 year of treatment that has significant effects on the subjective visual performance over the next day of skipping lens wear. Light distortion under low-light conditions seems to be a transient complication of the treatment and most of the patients report an improvement after the first weeks of treatment.Supported in part by projects PTDC/SAU-BEB/098391/2008//FCOMP-01-0124-FEDER-010897 and PTDC/SAU-BEB/098392/2008//FCOMP-01-0124-FEDER-010898 funded by Fundacao para a Ciencia e Tecnologia (FCT) of Portugal

Automatic classification of new articles in Spanish

We apply machine learning techniques to the automatic classification of news articles from the local newspaper La Capital of Rosario, Argentina. The corpus (LCC) is an archive of approximately 75,000 manually categorized articles in Spanish published in 1991. We benchmark on LCC three widely used supervised learning methods: k-Nearest Neighbors, Na¨ ve Bayes and Arti ficial Neural Networks, illustrating the corpus properties.Eje: V - Workshop de agentes y sistemas inteligentesRed de Universidades con Carreras en Informátic

Automatic classification of new articles in Spanish

We apply machine learning techniques to the automatic classification of news articles from the local newspaper La Capital of Rosario, Argentina. The corpus (LCC) is an archive of approximately 75,000 manually categorized articles in Spanish published in 1991. We benchmark on LCC three widely used supervised learning methods: k-Nearest Neighbors, Na¨ ve Bayes and Arti ficial Neural Networks, illustrating the corpus properties.Eje: V - Workshop de agentes y sistemas inteligentesRed de Universidades con Carreras en Informátic

Corrigendum to “Short-term changes in light distortion in orthokeratology subjects"

Artigo completo publicado na revista "BioMed Research International, (2015), 1-7" e disponível no RepositóriUM em: http://hdl.handle.net/1822/33375This study has been funded by FEDER through the COMPETE Programand by the Portuguese Foundation for Science and Technology (FCT) in the framework of projects PTDC/ SAU-BEB/098391/2008 and PTDC/SAU-BEB/098392/2008 and the Strategic Project PEST-C/FIS/UI607/2011