Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992a%26a...262l...1m&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 262, no. 1, p. L1-L4.
Astronomy and Astrophysics
Astrophysics
48
Galactic Evolution, Oxygen, Solar Neighborhood, Star Formation, Stellar Composition, Abundance, Galactic Halos
Scientific paper
We show that models for the chemical evolution of the solar neighborhood, adopting different star formation laws, produce a different behavior of the (O/Fe) in halo stars. In particular, we show that a change in slope in the (O/Fe) ratio occurring at (Fe/H) = -1.7, as claimed recently by Bessel et al. (1991), can be naturally reproduced by a model where the star formation rate is almost linear with gas density and the iron production from massive stars is lower than previously assumed. On the other hand, a squared dependence of the star formation rate on the gas density will produce an almost constant (O/Fe) ratio between -3 and -1 in (Fe/H). We predict that this behavior should be observed also in the other alpha-elements and that the (alpha/Fe) ratios should increase between (Fe/H) = -3.0 and -4.0, irrespective of the assumed star formation rate. The deduced timescale for the formation of the halo is about 1.4 Gyrs in our best model, where an almost linear dependence of the star formation rate on the gas density is assumed, and about 3 x 10 exp 8 yr in the other model. More precisely, this time scale should be the time of formation of the inner halo and it increases for the outer halo.
François Patrick
Matteucci Francesca
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