Seminars and Colloquia at ESO/Santiago

For ESO and ESO-related Conferences and Workshops in Europe and Chile please check the main Conferences and Workshops page.


Broadcast of the ESO talks is available upon request.  If anyone is interested, kindly contact us via email
at least 30 min prior  to the beginning of the talk.


October 2014

1.10.14 (Wednesday)
15:30
"Probing the nature of the First Stars: the role of the isotopic ratios of barium"
Gabriele CESCUTTI (INAF)
Abstract
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"Probing the nature of the First Stars: the role of the isotopic ratios of barium"

Gabriele CESCUTTI (INAF)

Abstract

In the last years our group has found that many chemical anomalies observed in very metal-poor halo stars suggest the first stellar generations to have been fast rotators (spinstars). Recently, theoretical computations have found that spinstars can also play a role in the chemical enrichment of neutron capture elements providing a early contribution of s-process. By means of a stochastic chemical evolution model, it is possible to identify the spinstars s-process contribution as the missing component responsible for the spread in the ratio between light (Sr) to heavy (Ba) neutron capture elements. A specific distribution is predicted for the isotopic ratio of Ba in halo stars and this imprint could be the smoking gun of the role played by spinstars in the spread of [Sr/Ba] ratio.

3.10.14 (Friday)
12:00
"Mean velocity flows as dynamical signatures of spiral structure in the Milky Way"
Benoit FAMAEY (Observatoire Astronomique de Strasbourg)
Abstract
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"Mean velocity flows as dynamical signatures of spiral structure in the Milky Way"

Benoit FAMAEY (Observatoire Astronomique de Strasbourg)

Abstract

In an equilibrium axisymmetric galactic disc, the mean galactocentric radial and vertical velocities are expected to be zero everywhere. In recent years, various large spectroscopic surveys, including the RAVE survey, have however shown that stars of the Milky Way disc exhibit nonzero mean velocities outside of the Galactic plane in both the Galactocentric radial and vertical velocity components. While radial velocity structures are commonly assumed to be associated with nonaxisymmetric components of the potential such as spiral arms or bars, nonzero vertical velocity structures are usually rather attributed to excitations by external sources such as a passing satellite galaxy or a small dark matter substructure crossing the Galactic disc. Through solutions of linearized Jeans equations for a zero velocity-dispersion population, and through 3D test-particle simulations, I however show that the global stellar response to a spiral perturbation induces both a radial velocity flow and nonzero vertical motion, and that the resulting structure of the mean velocity field is qualitatively similar to what is observed across the Milky Way disc.


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