9,878 research outputs found
Stellar Populations with ELTs
The star formation, mass assembly and chemical enrichment histories of
galaxies, and their present distributions of dark matter, remain encoded in
their stellar populations. Distinguishing the actual distribution functions of
stellar age, metallicity and kinematics at several locations in a range of
galaxies, sampling across Hubble types and representative environments, is the
information required for a robust description of galaxy histories. Achieving
this requires large aperture, to provide the sensitivity to reach a range of
environs and Hubble types beyond the Local Group, to provide high spatial
resolution, since the fields are crowded, and preferably with optical
performance since age-sensitivity is greatest near the main-sequence turn-off,
and metallicity-sensitivity for these warm stars is greatest in the optical.Comment: IAU Symposium No. 232, eds P. Whitelock, B. Leidundgeit & M.
Dennefel
Galactic Bulges
We review current knowledge on the structure, properties and evolution of
galactic bulges, considering particularly common preconceptions in the light of
recent observational results.Comment: in press, Annual Review Astron. Astrophys. 35 1997. Plain tex, 9
figures included. Also available by anonymous ftp at
ftp://ftp.ast.cam.ac.uk/pub/gil
Chemistry and kinematics in the solar neighborhood: implications for stellar populations and for galaxy evolution
The immediate Solar neighborhood should be a fair sample of the local Galaxy. However, the chemical abundance distribution of long-lived disk stars very near the Sun contains a factor of five to ten more metal-poor stars, -1 \simlt {\rm [Fe/H]} \simlt -0.4 dex, than is consistent with modern star-count models of larger scale Galactic structure. The metallicity distribution of complete samples of long-lived stars has long been recognised as providing unique constraints on the early stages of chemical evolution of the Galaxy, so that one would like to resolve this anomaly. We present a new derivation of the local G-dwarf metallicity distribution, based on the Third Gliese catalog combined with Olsen's (1983) Str\"omgren photometry. Kinematic data for these same stars, as well as for a high-precision sample studied by Edvardsson {\sl et al.} (1993), provide clear evidence that the abundance distribution below [Fe/H]\sim -0.4 contains two over-lapping distributions, the thick disk and the thin disk. We achieve a reliable deconvolution of the relative numbers in each population by comparing the local metallicity distribution with a recent determination (Gilmore, Wyse \& Jones 1995) of the metallicity distribution of F/G stars {\sl in situ} some 1500pc from the Sun. The gravitational sieve of the Galactic potential acts on this second sample to segregate the low velocity dispersion, thin-disk, component of the local sample, leaving predominantly the second, higher velocity dispersion component. The combination of these two datasets allows us to determine the source of the local paradox: there is a substantial tail of the thin disk (defined kinematically) metallicity distribution, which extends below {\rm [Fe/H] \approx -0.4}dex. This is a robust conclusion, being consistent with the sum of star count, stellar spatia
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