Optical spectroscopy of the Be/X-ray binary V850 Centauri/GX 304-1 during faint X-ray periodical activity

Context. Be/X-ray binaries (BeXRBs) are the most populous class of high-mass X-ray binaries. Their X-ray duty cycle is tightly related to the optical companion wind activity, which in turn can be studied through dedicated optical spectroscopic observations. Aims. We study optical spectral features of the Be circumstellar disk to test their long-term variability and their relation with the X-ray activity. Special attention has been given to the Hα emission line, one of the best tracers of the disk conditions. Methods. We obtained optical broadband medium resolution spectra from a dedicated campaign with the Anglo-Australian Telescope and the Southern African Large Telescope in 2014−2015. Data span over one entire binary orbit, and cover both X-ray quiescent and moderately active periods. We used Balmer emission lines to follow the evolution of the circumstellar disk. Results. We observe prominent spectral features, like double-peaked Hα and Hβ emission lines. The HαV/R ratio significantly changes over a timescale of about one year. Our observations are consistent with a system observed at a large inclination angle (i ≳ 60°). The derived circumstellar disk size shows that the disk evolves from a configuration that prevents accretion onto the neutron star, to one that allows only moderate accretion. This is in agreement with the contemporary observed X-ray activity. Our results are interpreted within the context of inefficient tidal truncation of the circumstellar disk, as expected for this source’s binary configuration. We derived the Hβ-emitting region size, which is equal to about half of the corresponding Hα-emitting disk, and constrain the luminosity class of V850 Cen as III–V, consistent with the previously proposed class

Compreensão textual em alunos de segunda e terceira séries: uma abordagem cognitiva Text comprehension in second and third graders: a cognitive approach

Este estudo teve como objetivo analisar a compreensão de leitura textual de alunos de 2ª e 3ª séries. Participaram 76 crianças, com média de idade de 8,1 anos. Cada criança lia a história, recontava-a e, posteriormente, respondia a questões. Os recontos foram analisados segundo o Modelo de Compreensão Textual de Kintsch & van Dijk (1978) e Kintsch (1988, 1998). A amostra relatou, em média, 21,07% da estrutura proposicional da história, sendo mais freqüente o relato de macroproposições. Alunos da terceira série foram superiores aos da segunda série no relato de microproposições menos relevantes do texto e em responder a questões pontuais sobre a história. Foi encontrada uma correlação significativa entre idade e o reconto da macroestrutura textual. Os resultados sugerem que durante os primeiros anos de escolarização ocorreu uma melhora da memorização de detalhes, enquanto que a retenção das idéias essenciais foi influenciada pelas variações de idade das crianças.<br>This study aimed to analyze text comprehension of students of the 2nd and 3rd grades. The sample was constituted by 76 children, at an average of 8.1 years old. Each child read the story, retold it and, afterwards, answered questions about it. The retellings were analyzed according to the model of Text Comprehension of Kintsch and van Dijk (1978) and Kintsch (1988, 1998). The sample recalled a mean of 21.07% of the proposition structure of the story, being the report of macropropositions more frequent. Students of the third grade told larger percentage of irrelevant micropropositions of the text and they were superior in answering to specific questions than students of the second grade. A significant correlation was found between age and macroproposition's retelling. The results suggest that during the first years of schooling there is an improvement of the detail-remembering, whereas the retention of the essential ideas is influenced by age differences