Chemodynamics of the Milky Way. I. (Anders et al.)

Vol. 564
In section 10. Galactic structure, stellar structure and populations

Chemodynamics of the Milky Way. I. The first year of APOGEE data

by F. Anders, C. Chiappini, B. X. Santiago, et al., A&A 564, A115


In this paper, the first year of APOGEE (Apache Point Observatory Galactic Evolution Experiment) data, 57 000 red giant branch stars are used to investigate the chemo-dynamical properties of the disk of the Milky Way. This multi-object high-resolution near-infrared spectroscopic survey is able to peer through the dust that obscures stars in the Galactic disk and bulge at optical wavelengths. The sample extends up to 10kpc from the Sun, but the majority of red giants observed are at a distance of 1-6kpc from the Sun. This study increases the number studied in this way (by the RAVE and SEGUE surveys) by a factor 8. These results confirm a gap in the Fe-alpha diagram. That the number of stars with high-alpha/fe ratios decreases toward the outer parts of the Galactic disk suggests that the scale length of the thick disk is shorter than that of the thin disk. For stars high above the plane, with 1.5 < z < 3 kpc a positive metallicity gradient and a negative gradient in [ alpha/Fe] is reported.