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ASTR 5610, Majewski [SPRING 2012]. Lecture Notes

ASTR 5610 (Majewski) Lecture Notes


SURVEY OF KINEMATICAL PROPERTIES OF MILKY WAY POPULATIONS







UPDATES WITH NEW RESULTS BASED ON CHEMICAL DISCRIMINATION OF THIN/THICK DISK STARS

We have "complained" up to now that it is very difficult to discriminate thick disk stars from thin and halo populations, which overlap in metallicity, kinematical and spatial distributions.

But something very interersting has been surfacing recently in studies of the detailed chemical properties of Galactic stars. It has become apparent that, at least in the solar neighborhood, thick disk stars are enhanced in [α / Fe] compared to thin disk stars:

Figure from Schonrich & Binney 2009, MNRAS. The bottom panel is a collation of quality data on nearby stars. Note the distinct gap showing up in the transition region from high [α / Fe] to low [α / Fe]. Model data for the formation of the thick disk from radial migration, shown in the top panel, shows a suggested separation of thin disk stars in the lower, high density ridge (outlined in black line). Green points mark stars having the kinematical character of thick disk stars in the model.

Yet another division of the observational plane of chemical abundances into proposed "thin disk" and "thick disk" populations, by Young Sun Lee et al. 2011, using large samples of (17.277) SDSS SEGUE data on nearby G stars.
The origin of the gap in these distributions aside for the moment (see thick disk origin lecture), the proposed division of stars yields interesting results that are highly suggestive that a viable way of discriminating local thin and thick disk stars may exist through this chemical division.

Here are some of those interesting results, from Lee et al. (2011):


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All material copyright © 2003 Steven R. Majewski. All rights reserved. These notes are intended for the private, noncommercial use of students enrolled in Astronomy 551 at the University of Virginia.