Radial migration of stars in the Galactic disk
1er juin 2008
The origin and importance of radial mixing of stars in the galactic thin disk are uncertain. At the sun galactocentric radius, stars move essentially on circular orbits around the Galaxy, but they may be shifted radially because of various dynamical processes (spiral arms). Two recent articles written by an astronomer from Paris Observatory reveal the imprint of radial mixing on the kinematics of stars in the solar neighbourhood, analysing several consequences.
One of these concerns the transition between the thick disk and the thin disk. The thick disk is composed of old stars of unknown origin. They could have been formed in the Galaxy, or have been accreted from a dwarf galaxy in the distant past of the Milky Way (more than 8-10 billion years). The abundance of alpha-elements as a function of metallicity (see figure) for stars in the solar neighbourhood shows that there exist a hiatus in metallicity between metal-rich stars of the thick disk (at about -0.2 dex) and metal-poor stars of the thin disk (at -0.8<[Fe/H]
<-0.6>
Note : the metallicity measures the abundance of elements heavier than hydrogen and helium in the atmosphere of stars. It is given relatively to the sun own abundance. Alpha elements are synthetized in massive stars and have a nucleus, the mass of which is a multiple of that of helium (alpha particule). Ca, Mg, Si, and Ti alpha-elements have been used in these studies.
References Haywood, 2008, MNRAS in presse, Radial mixing and the transition between the thick and thin Galactic discs http://arxiv.org/abs/0805.1822 Haywood 2008 A&A 482, 673, A peculiarity of metal-poor stars with planets ? http://arxiv.org/abs/0804.2954
Contact Misha Haywood (Observatoire de Paris, GEPI)
Dernière modification le 4 mars 2013