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Orbits in a Milky Way with a massive thick disk : A new Galactic model for orbit computations

Proposition de stage au niveau M1.

Proposant : Paola Di Matteo (GEPI).

Sujet : The study of the trajectory of stars and stellar systems in the Milky Way, like globular and open clusters, is an essential tool to understand the properties of the different Galactic stellar populations (thin and thick disks, stellar halo) and their mode of formation.

To integrate stellar orbits, one needs simple, fully analytical and realistic models of the mass distribution in the Milky Way. Such models have been developed in the past (see for example Allen & Santillan 1991), and allow to reconstruct the orbits of stars and stellar systems, if radial velocities, proper motions and distances are available.

However, there is growing evidence that the mass distribution in the Milky Way may be significantly different from what has been proposed in the last 20 years. Indeed, recent results point out to the presence of a thick disk, as massive as the thin disk, and to a negligible contribution of a classical bulge to the overall mass budget. In this stage, we propose to explore a new model of the Galactic mass distribution which implements a massive thick disk — something completely disregarded in models so far — with properties in agreement with the most recent observational determinations.

The aim of this work is to reconstruct orbits of known stars in the Galaxy, to quantify to what extent the presence of a massive thick disk component can affect them, and ultimately to reconstruct the links between Galactic stellar populations, making use of the kinematic information derived from the orbit integrations, and link them to known chemical properties.