Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21341602l&link_type=abstract
American Astronomical Society, AAS Meeting #213, #416.02; Bulletin of the American Astronomical Society, Vol. 41, p.227
Astronomy and Astrophysics
Astrophysics
3
Scientific paper
Ever since the Milky Way's thick disk was identified as a distinct component by star counts, astronomers have attempted to understand its origin. The current possible scenarios for its formation include heating of a pre-existing thin disk through mergers, or a scenario whereby thick-disk stars were accreted from small satellites that encountered the Galaxy in the past. Numerical simulations also suggest that the thick disk may have formed through chaotic mergers of gas-rich systems. It cannot be ruled out that all three of the above possibilities played a role in the formation of the thick disk. The kinematics and elemental abundance ratios of thick-disk stars have been used to establish its distinct properties (such as scale height, mean rotational velocity, star formation history, etc.) from the other constituents (thin disk and halo) of the Galaxy. Although providing valuable information for disentangling the formation of the thick disk on the basis of detailed chemical information, the requirement for high-resolution spectroscopy has limited the sizes of many previous samples. Here we estimate accurate radial velocities, metallicities, temperatures, surface gravities, α-abundances, and distances, using the SEGUE Stellar Parameter Pipeline, for an unbiased sample of 70,000 thin and thick disk stars with medium resolution ( 2.5 A), originally targeted as F- and G-type stars in SEGUE. We combine this information with proper motions derived from the re-calibrated USNOB-2 catalog to present a kinematic and chemical abundance analysis of the sample, and examine its constraints on the origin of the thick-disk population. This work was supported in part by grants PHY 02-16783 and PHY 08-22648: Physics Frontiers Center / Joint Institute for Nuclear Astrophysics (JINA), awarded by the U.S. National Science Foundation.
Beers Timothy C.
Lee Young Sam
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