Concluding remarks and open questions

• A model in which the thick and thin disks form on different timescales (around 0.8 and 7 Gyr, respectively) can well explain the observed differences between the abundance ratios of thick- and thin-disk stars, for several elements, as a function of metallicity.

-0.2 0 [O/H]

.1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1. L [Sc/Fe] J

.i i i i 1 i i i i 1 i i i i 1 i i i. L [Co/Fe] J

. ~

.i i i i 1 i i i i 1 i i i i 1 i i i. [V/Fe]

" - 1*- *-ti **

- i i i ... -

"... i i i .. "

.i i i i 1 i i i i 1 i i i i 1 i i i. L [Cr/Fe] J

.i i i i 1 i i i i 1 i i i i 1 i i i. [Cu/Fe]

... I I I .. ~

... 1 1 1 ■ ■ "

rTTrrTTTTTi^^i^T^

L [Zn/Fe] J ; - "it*«..^.

Figure 47.3. Comparing thick- and thin-disk abundance patterns predicted by model A. Left panel: [a/O] versus [O/H] diagrams showing data from Bensby et al. (2003, 2004, 2005) for thin (light pentagons) and thick (black pentagons) disks. Right panel: [iron-peak/Fe] versus [Fe/H] diagrams. The data are again from Bensby et al. (pentagons) and from Brewer & Carney (2006) (triangles - open for thin-disk and closed for thick-disk stars).

• There is still no agreement on how metal-rich the thick disk is (does it extend to metal-licities above Solar?). The answer to this question is important in order to constrain the late phases of the star-formation history of the thick disk.

• Are the over-Solar-metallicity stars in the Bensby et al. sample thin-disk stars from the Solar vicinity? According to our models, with current stellar yields, and given the other constraints, the thin disk stars with [Fe/H] > 0.2 should have come from an inner region of the disk. A curve for 4 kpc would fit these data well - see Selwood & Binney (2002) and Grenon (1999) for dynamical effects that might cause radial migration of stars.

• Taking together the high-quality data now available for the thin- and thick-disk and halo stars, we have the opportunity to better constrain the stellar yields and their dependencies on metallicity.

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