"Seminários Acadêmicos de Física e Astronomia" Seminário 1: "Apenas seis números: o tamanho da nossa ignorancia"

Esta palestra está montada sobre uma reflexão de Martin Rees. Nela abordamos a síntese atual do conhecimento da Física e da Astronomia aplicados a dimensões que vão do tamanho dos átomos ao do Universo. Este conhecimento pode ser sintetizado em 6 números. Dois que determinam a estabilidade do micro-cosmos (átomos, núcleos atómicos, etc), dois que determinam a estabilidade do Universo em escalas cósmicas e dois que determinam a textura do Universo. Comentamos os degraus superados pela ciência a partir dos trabalhos de Galileu considerado o iniciador do método científico moderno.

Seminário 2: "Star formation in grand-design, spiral galaxies: young, massive clusters in the near-infrared" H. Dottori & P. Grosbol

Aims. Spiral structure is a prominent feature in many disk galaxies and is often outlined by bright, young objects. The objective is to study the distribution of young stellar clusters in grand-design spiral galaxies and thereby determine if strong spiral perturbations can influence star formation.

Methods. Deep, near-infrared JHK-maps were observed for 10 nearby, grand-design, spiral galaxies using HAWK-I at the VLT. Complete, magnitude limited candidate lists of star forming complexes were obtained by searching the K-band maps. The properties of the complexes were derived from (H-K)–(J-H) diagrams including

identification of the youngest ones (i.e. <∼7Myr) and estimation of their extinction.

Results. Young stellar clusters with ages <∼7Myr have significant internal extinction in the range of AV=3-7m while older ones typically have AV< 1m. The cluster luminosity function (CLF) is well fitted by a power law with an exponent around -2 and no evidence of a high luminosity cut-off was found. The brightest cluster complexes in the disk reach luminosities of MK = -15. m 5 or estimated masses of 10^6M⊙. At radii with a strong, two-armed spiral pattern, star formation in the arms is enhanced by a factor of 2-5 compared to that in the inter-arm regions. The CLF in the arms is also shifted to brighter MK by at least 0.4m. We also detect clusters with colors compatible with LMC intermediate and Milky Way globular cluster ages. The (J-K)-MK diagram of several galaxies shows, for the brightest clusters, a clear separation between young clusters highly attenuated by dust and older ones with low extinction.

Conclusions. The gap in (J-K)-MK diagrams suggests a rapid expulsion of dust at an age around 7Myr possibly triggered by supernovae. The existence of strong spiral perturbations concentrates the formation of clusters in the arm regions and shifts their CLF towards brighter magnitudes.