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March 2013
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Colloquium Héloïse Meheut (CEA Saclay)

Friday 15 March 2013 11:00-12:00

The Rossby Wave Instability: From Microquasars to Planets (Héloïse Meheut, CEA Saclay)

The most challenging step in planet formation theory is to explain the formation of planetesimals of kilometre size. A promising scenario involves the existence of vortices able to concentrate a large amount of dust grains in their centres and to accelerate the growth of the solids.

Here we are interested in the Rossby wave instability that can form vortices against the shearing effect of differential rotation. I will present numerical simulations of this instability, initially performed in the context of microquasars accretion disks and emission of jets. I will then show why the unexpected results of these simulations were applied to the study of protoplanetary disks and how it modified our understanding of planetesimals formation.

Colloquium C. Charbonnel : Multiple stellar populations in globular clusters and massive star clusters

Friday 22 March 2013 11:00-12:00

Multiple stellar populations in globular clusters and massive star clusters: Formation, evolution, dynamics

A major paradigm shift has recently revolutionized our picture of
globular clusters (GC) that were long thought to be simple systems of
coeval stars born out of homogeneous material. Indeed, detailed
abundance studies of GC long-lived low-mass stars performed with 8-10m
class telescopes, together with high-precision photometry of Galactic
GCs obtained with HST, have brought compelling clues on the presence of
multiple stellar populations in individual GCs. These stellar subgroups
can be recognized thanks to their different chemical properties (more
precisely by abundance differences in light elements from carbon to
aluminium) and by the appearance of multimodal sequences in the
colour-magnitude diagrams.

This has a severe impact on our understanding of the formation and early
evolution of GCs, and more generally of the role that massive stars may
play in shaping the intra-cluster medium and in inducing secondary star
formation in massive star clusters.
In this talk I will summarize the observational status and present the
detailed timeline we have recently proposed for the first 40 Myrs in the
lifetime of a typical massive protocluster following the general ideas
of our so-called "Fast Rotating Massive stars scenario" and taking into
account the dynamics of interstellar bubbles produced by stellar winds
and supernovae. I will also discuss various implications of this
new paradigm on the determination of the fraction of Galactic halo stars
that may have originated in massive star clusters, as well as on the
estimate of the contribution of GCs to cosmic reionisation.

Colloquium Di Li "FAST: The Promise of the Next Giant Radio Telescope"

Friday 29 March 2013 11:00-12:00

The National Astronomical Observatories (NAOC) has started building the largest antenna in the world. Known as FAST, the Five-hundredmeter Aperture Spherical radio Telescope is a Chinese mega-science project funded by the National Development and Reform Commission (NDRC). FAST also represents part of Chinese contribution to the international efforts to build the square kilometer array (SKA). Upon its finishing around September of 2016, FAST will be the most sensitive single-dish radio telescope in the low frequency radio bands between 70 MHz and 3 GHz. I will review the design specifications of FAST, its expected capabilities, and its main scientific aspirations. In anticipation of the likely limitations at the initial stages of operation, I will also discuss the considerations and opportunities for astronomical discoveries in the "early science" phase of FAST. Finally, a brief introduction of the pilot projects currently being carried out at Arecibo and GBT to help refine the science plans in the FAST frequency range.

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