Galaxy thin disk

Abstract. We have investigated the abundance of several chemical elements in two large stellar samples kinematically representative of the thin and the thick disks of the Galaxy. Chemical, kinematical and age data have been collected from high quality sources in the literature. Velocities (U,V,W) have been computed and used to select stars with the highest probability to belong to the thin disk and the thick disk respectively. Our results show that the two disks are chemically well separated. Both exhibit a decline of [a/Fe] with increasing [Fe/H]. A transition between the thin/thick disks stars is observed at 10 Gyr... 

Abstract. In an effort to determine accurate stellar parameters and abundances for a large sample of nearby stars, we have performed the detailed analysis of 350 high-resolution spectra of FGK dwarfs and giants. This sample will be used to investigate behavior of chemical elements and kinematics in the thick and thin disks, in order to better constrain models of chemical and dynamical evolution of the Galaxy. 

What happened to the gas expelled from the halo A traditional answer based on monolithic models of a Galaxy collapsing through successive stages of halo, thick disk and thin disk would be that the expelled gas formed the raw material of the disk. This hypothesis faces some severe difficulties. For one thing, the remaining mass in the halo should then be about 10 per cent of the mass of the disk, whereas it is probably a factor of 5 or so less than this (Carney, Latham Laird 1990). Another difficulty is the specific angular momentum, as is apparent qualitatively from Fig. 8.15 and is illustrated quantitatively in Fig. 8.21. 

Figure 1. Spatial distribution of NSs in the Galaxy. The data was calculated by a Monte-Carlo simulation. The kick velocity was assumed following Arzoumanian et al. (2002). NSs were born in a thin disk with a semithickness 75 pc. Those NS that were bom inside R = 2 kpc and outside R = 16 kpc were not taken into account. NS formation rate was assumed to be constant in time and proportional to the square of the ISM density at the birthplace. Results were normalized to have in total 5 x 108 NSs born in the described region. Density contours are shown with a step 0.0001 pc 3. At the solar distance from the center close to the galactic plane the NS density is about 2.8 1CT4 pc 3. From Popov et al. (2003a).

Abundances and Ages of the Deconvolved Thin/Thick Disks of the Galaxy... 

When the metallicity distribution of damped Lya systems is compared with those of different stellar populations of the Milky Way, we find that is broader and peaks at lower metallicities than those of either thin or thick disk stars (Figure 8). At the time when our Galaxy s metal enrichment was at levels typical of DLAs, its kinematics were closer to those of the halo and bulge than a rotationally supported disk. This finding is at odds with the proposal that most DLAs are large disks with rotation velocities in excess of 200 km s 1, put forward by Prochaska Wolfe (1998). 

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