Sub-giant stars as tracers of galactic chemical evolution
The low luminosities of dwarf stars and the modest sizes of most telescopes used
for studies of galactic chemical evolution until recently clearly limit the
volume of the Galaxy available for study.
Although some stars with distant birth places are likely to visit the solar
vicinity, a less model-dependent study of the galactic chemical evolution
requires in situ study of the detailed properties of different stellar
environments: fields within and outside the "solar circle", fields in the
galactic halo and the bulge as well as globular cluster fields.
The new class of very large telescopes
(e.g. ESO's Very Large Telescope, VLT),
with, high resolution spectrographs will considerably extend the volume available
for such studies of dwarf stars.
In order to further extend the range of such studies it is important also to
use more luminous stars without loosing accuracy in the derived abundances.
In a project managed by my PhD student
we are therefore making a systematic exploratory
study of sub-giant stars of different metallicities in order to evaluate their
specific usefulness for accurate galactic chemical evolution studies.
Except for being more luminous than dwarfs, sub-giant stars have the important
advantage over most dwarf stars that their ages may be determined by means of
This is necessary for the chronological aspects.
We have obtained high-resolution spectra with the CES spectrograph fed by the
1.4m CAT telescope of the
European Southern Observatory
and the SOFIN spectrograph of the 2.5m
Nordic Optical Telescope,
of 35 sub-giant field stars
spanning metallicities, [Fe/H], from about -2.0 to +0.3.
The analysis has been started and the spectra will enable abundance
determinations for a wide range of chemical elements: CNO, "alpha" elements,
iron-peak elements, s- and r-process elements.
Lithium (which is thought to be affected by mixing and destruction processes in
these stars) will also be searched for.
Latest update: June 2, 2000