Mass distribution and structural parameters of Small Magellanic Cloud star clusters

In this work we estimate, for the first time, the total masses and mass function slopes of a sample of 29 young and intermediate-age SMC clusters from CCD Washington photometry. We also derive age, interstellar reddening and structural parameters for most of the studied clusters by employing a statistical method to remove the unavoidable field star contamination. Only these 29 clusters out of 68 originally analysed cluster candidates present stellar overdensities and coherent distribution in their colour-magnitude diagrams compatible with the existence of a genuine star cluster. We employed simple stellar population models to derive general equations for estimating the cluster mass based only on its age and integrated light in the B, V, I, C and T1 filter. These equations were tested against mass values computed from luminosity functions, showing an excellent agreement. The sample contains clusters with ages between 60 Myr and 3 Gyr and masses between 300 and 3000 Mo distributed between ~0.5 deg. and ~2 deg. from the SMC optical centre. We determined mass function slopes for 24 clusters, of which 19 have slopes compatible with that of Kroupa IMF (2.3 +/- 0.7), considering the uncertainties. The remaining clusters - H86-188, H86-190, K47, K63 and NGC242 - showed flatter MFs. Additionally, only clusters with masses lower than ~1000 Mo and flatter MF were found within ~0.6 deg. from the SMC rotational centre.Comment: 12 pages, 19 figures. Includes another 29 full-page figures of supplementary material. Accepted for publication in the MNRA

Oficina Jun Ji, por exemplo!

O espólio de pranchas xilográficas da Oficina Jun Ji (Cant. Kuan Kei) de Foshan, recolhido nos anos 80 no Museu da Cidade, parece constituir o mais representativo conjunto de antigas pranchas de impressão existente na província de Cantão. Esta comunicação, baseada no corpus de 29 reedições feitas pelo Museu nos finais dos anos 80 ou inícios de 90, aplica pela primeira vez critérios quantificados à interpretação de conjuntos de gravura chinesa. Em termos iconográficos, a oficina Jun Ji aparece-nos como “exemplar”, abrangendo a sua produção quase todos os temas conhecidos na gravura ritual de FoshanThis paper studies 29 prints (or pairs of prints) from the Jun Ji workshop, reissued in the late 80’s by the Foshan City Museum. For the first time quantitative methods were used to compare this workshop with the others in the province and with the rest of China. The percentage of writen characters per print, the occurence of certain symbols and the phenomenon of intentionaly obliterating shopmarks in the printing plates. The aspects that came out of that study were, among others, 1) the antithetical (not just simetrical) value of most of the Jun Ji door gods, 2) the provincial use of the bagua as opposed to the national use of the taiji, and 3) the large numbers of anonymised Foshan prints, probably linked with smuggling to Hong Kong and Maca

The Seyfert Population in the Local Universe

The magnitude-limited catalog of the Southern Sky Redshift Survey (SSRS2), is used to characterize the properties of galaxies hosting Active Galactic Nuclei. Using emission-line ratios, we identify a total of 162 (3%) Seyfert galaxies out of the parent sample with 5399 galaxies. The sample contains 121 Seyfert 2 galaxies and 41 Seyfert 1. The SSRS2 Seyfert galaxies are predominantly in spirals of types Sb and earlier, or in galaxies with perturbed appearance as the result of strong interactions or mergers. Seyfert galaxies in this sample are twice as common in barred hosts than the non-Seyferts. By assigning galaxies to groups using a percolation algorithm we find that the Seyfert galaxies in the SSRS2 are more likely to be found in binary systems, when compared to galaxies in the SSRS2 parent sample. However, there is no statistically significant difference between the Seyfert and SSRS2 parent sample when systems with more than 2 galaxies are considered. The analysis of the present sample suggests that there is a stronger correlation between the presence of the AGN phenomenon with internal properties of galaxies (morphology, presence of bar, luminosity) than with environmental effects (local galaxy density, group velocity dispersion, nearest neighbor distance).Comment: 35 pages, 13 figures, Accepted to be publised in Astronomical Journa

Casimir torque between corrugated metallic plates

We consider two parallel corrugated plates and show that a Casimir torque arises when the corrugation directions are not aligned. We follow the scattering approach and calculate the Casimir energy up to second order in the corrugation amplitudes, taking into account nonspecular reflections, polarization mixing and the finite conductivity of the metals. We compare our results with the proximity force approximation, which overestimates the torque by a factor 2 when taking the conditions that optimize the effect. We argue that the Casimir torque could be measured for separation distances as large as 1 $\mu{\rm m}.$Comment: 7 pages, 3 figures, contribution to QFEXT07 proceeding

Avaliação da precipitação projetada pelos modelos do IPCC-AR4 para o Nordeste e o Sudeste do Brasil.

Resumo: Alterações na precipitação e na temperatura levam a modificações no escoamento superficial e na disponibilidade de água. Para se projetar prováveis cenários de alterações climáticas no futuro, os modelos de circulação global (GCMs) são considerados a melhor ferramenta, apesar das suas incertezas. As projeções de precipitação pluviométrica de quinze GCMs do Intergovernamental Panel on Climate Change (IPCC) - Fourth Assessment Report (AR4) foram avaliadas para as regiões Nordeste e Sudeste do Brasil, no período de 2071 a 2100, cenário de emissão A2. Foram realizadas análise de componentes principais e análise de agrupamento hierárquico para agrupar os modelos quanto à similaridade espacial das projeções da chuva acumulada, após correção de viés, para cada estação. Similaridades espaciais variaram entre as estações

GeMs/GSAOI observations of La Serena 94: an old and far open cluster inside the solar circle

Physical properties were derived for the candidate open cluster La Serena 94, recently unveiled by the VVV collaboration. Thanks to the exquisite angular resolution provided by GeMS/GSAOI, we could characterize this system in detail, for the first time, with deep photometry in JHK$_{s}$ - bands. Decontaminated JHK$_{s}$ diagrams reach about 5 mag below the cluster turnoff in H. The locus of red clump giants in the colour - colour diagram, together with an extinction law, was used to obtain an average extinction of $A_V =14.18 \pm 0.71$. The same stars were considered as standard - candles to derive the cluster distance, $8.5 \pm 1.0$ kpc. Isochrones were matched to the cluster colour - magnitude diagrams to determine its age, $\log{t(yr)}=9.12\pm 0.06$, and metallicity, $Z=0.02\pm0.01$. A core radius of $r_{c}=0.51\pm 0.04$ pc was found by fitting King models to the radial density profile. By adding up the visible stellar mass to an extrapolated mass function, the cluster mass was estimated as $M=(2.65\pm0.57) \times 10^3$ M$_{\odot}$, consistent with an integrated magnitude of $M_{K}=-5.82\pm0.16$ and a tidal radius of $r_{t}=17.2\pm2.1$ pc. The overall characteristics of La Serena 94 confirm that it is an old open cluster located in the Crux spiral arm towards the fourth Galactic quadrant and distant $7.30\pm 0.49$ kpc from the Galactic centre. The cluster distorted structure, mass segregation and age indicate that it is a dynamically evolved stellar system.Comment: 16 pages, 24 figures, 2 Tables, accepted by MNRAS; corrected typo