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Astron. Astrophys. 358, 671-681 (2000)

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Abundances of light elements in metal-poor stars

IV. [Fe/O] and [Fe/Mg] ratios and the history of star formation in the solar neighborhood

R.G. Gratton 1, E. Carretta 1, F. Matteucci 2,3 and C. Sneden 4

1 Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
2 Università di Trieste, Dipartimento die Astronomia, Via G.B. Tiepolo 11, 31413 Trieste, Italy
3 SISSA/ISAS, via Beirut, 34014 Trieste, Italy
4 University of Texas at Austin and McDonald Observatory, USA

Received 28 February 2000 / Accepted 17 April 2000


The accurate O, Mg and Fe abundances derived in previous papers of this series from a homogeneous reanalysis of high quality data for a large sample of stars are combined with stellar kinematics in order to discuss the history of star formation in the solar neighborhood. We found that the Fe/O and Fe/Mg abundance ratios are roughly constant in the (inner) halo and the thick disk; this means that the timescale of halo collapse was shorter than or of the same order of typical lifetime of progenitors of type Ia SNe ([FORMULA] Gyr), this conclusion being somewhat relaxed (referring to star formation in the individual fragments) in an accretion model for the Galaxy formation. Both Fe/O and Fe/Mg ratios raised by [FORMULA] dex while the O/H and Mg/H ratios hold constant during the transition from the thick to thin disk phases, indicating a sudden decrease in star formation in the solar neighbourhood at that epoch. These results are discussed in the framework of current views of Galaxy formation; they fit in a scenario where both dissipational collapse and accretions were active on a quite similar timescale.

Key words: stars: abundances – nuclear reactions, nucleosynthesis, abundances – Galaxy: evolution

Send offprint requests to: R.G. Gratton

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© European Southern Observatory (ESO) 2000

Online publication: June 8, 2000