CCD uvbyβ photometry of faint stars. III. Metallicities and ages of F-stars in the Galactic disk.

Details CCD uvbyβ photometry of faint stars. III. Metallicities and ages of F-stars in the Galactic disk. CCD uvbyβ photometry of faint stars. III. Metallicities and ages of F-stars in the Galactic disk.

Jun 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...298..799j&link_type=abstract

Astronomy and Astrophysics, v.298, p.799

Astronomy and Astrophysics

Astrophysics

13

Galaxy: Abundances, Galaxy: Evolution, Galaxy: Fundamental Parameters, Galaxy: Structure, Galaxy: Stellar Content

Scientific paper

Stars as faint as V=~22^m^ have been observed in six selected directions of the Galaxy, the limiting magnitude of the sample of stars having the full uvbyβ information is approximately 18.5mag . Intrinsic colours and distances have been derived for 435 F-stars by Jonch-Sorensen (1994b) (Paper II) and in this paper metallicities and effective temperatures are estimated for these stars. Asample of these (318 stars) are found with δ m_0_ and δ c_0_ indices that permit ages to be estimated using theoretical isochrones. The majority of the stars have galactocentric distances, R, from approximately 2kpc to 12kpc and heights above the plane, z, below 2kpc. For the total sample no significant radial variation of metallicity is found for R from 5 to 11kpc, independently of z. A steepening of the radial gradient is indicated for R>9kpc, most prominent for the oldest age groups. The derived vertical metallicity gradient is =~-0.2dex for 3001kpc, or Stroemgren's definition of ipII or the age-z diagram a lower age limit of 5-6Gyr seems inevitable. Such a low age has been indicated before, but it is in conflict with most models of the formation of the disks of the Galaxy. Comparing the (b-y)-V diagrams for the different fields indicates the presence of a cut-off of the (thick) disk occurring at R>15. The results obtained in the present paper support a formation scenario in which the disk forms from `inside out' and a thick disk formation that probably is a combination of `top down' and `bottom up'.

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