A kinematic and abundance survey in the galactic rotational directions
Bell, David James
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https://hdl.handle.net/2142/22561
Description
Title
A kinematic and abundance survey in the galactic rotational directions
Author(s)
Bell, David James
Issue Date
1996
Doctoral Committee Chair(s)
Yoss, Kenneth M.
Department of Study
Astronomy
Discipline
Astronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Astronomy and Astrophysics
Language
eng
Abstract
"Photometric and spectroscopic observations have been obtained for 1028 G and K-type stars near the cardinal directions corresponding to Galactic rotation and anti-rotation. The spectra have been used to obtain radial velocities by cross-correlation, and estimates of stellar metallicity via a spectrophotometric index. The DDO and BV photometric observations yield estimates of distance, color excess, spectral type and metallicity. Reddening trends as a function of distance are found to be consistent with previous investigations in each of the two directions. An extracted subsample of 570 late-type giants has been used with maximum likelihood modeling to study the kinematic and abundance characteristics of the local Galactic disk. The data are well represented by a two-component disk model in which the ""thick disk"" has a mean abundance of $-0.35 \pm 0.06$, an asymmetric drift of $43 \pm 9$ km s$\sp{-1}$, and a local normalization of $13 \pm 3$%. A continuous ""extended disk"" model is also fitted to the data, but is found to be significantly inferior through a likelihood ratio test."
The discrete nature supports disk-formation models in which the thick disk is created by a separate distinguishable process relative to the thin disk, such as through a merger event early in the disk's history. It is less consistent with models in which the thick disk forms through continuous processes, such as during a dissipational disk collapse or through secular kinematic diffusion of stars from a thin-disk configuration into a thick one.
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