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Chemo-Kinematic Properties of the Galactic Disk with SEGUE G and K Dwarfs: Constraints on Formation

Published online by Cambridge University Press:  02 August 2018

Doori Han
Affiliation:
Department of Astronomy, Space Science, and Geology, Chungnam National University, Daejeon 34134, South Korea email: doori@cnu.ac.kr
Young Sun Lee
Affiliation:
Department of Astronomy and Space Science, Chungnam National University, Daejeon 34134, South Korea
Young Kwang Kim
Affiliation:
Department of Astronomy and Space Science, Chungnam National University, Daejeon 34134, South Korea
Timothy C. Beers
Affiliation:
Department of Physics & JINA-CEE, University of Notre Dame, Notre Dame, IN 46556, USA
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Abstract

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We present the derived kinematic characteristics of low-α thin-disk and high-α thick-disk stars in the Milky Way, investigated with a sample of about 32,000 G- and K-type dwarfs from the Sloan Extension for Galactic Understanding and Exploration (SEGUE). Based on the level of α-element enhancement as a function of [Fe/H], we separate our sample into thin- and thick-disk stars and then derive mean velocities, velocity dispersions, and velocity gradients for the U, V, and W velocity components, respectively, as well as the orbital eccentricity distribution. There are notable gradients in the V velocity over [Fe/H] in both populations: −23 km s−1 dex−1 for the thin disk and +44 km s−1 dex−1 for the thick disk. The velocity dispersion of the thick disk decreases with increasing [Fe/H], while the velocity dispersion gradient over [Fe/H] for the thin disk is almost flat for all velocity components, except for the W velocity dispersion of the metal-poor thin-disk stars. The eccentricity distribution exhibits a peak at a higher value, and is more symmetric as [α/Fe] increases, implying that complex formation mechanisms may be involved. Our results can be used to constrain several proposed disk-formation scenarios of the Milky Way and other large spirals.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2018 

References

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