A&A 416, 997-1011 (2004)
DOI: 10.1051/0004-6361:20034265

Neutron star mergers versus core-collapse supernovae as dominant r-process sites in the early Galaxy

D. Argast ^{1, 2}, M. Samland ², F.-K. Thielemann ¹ and Y.-Z. Qian <sup>3

1</sup>  Institut für Physik der Universität Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland
²  Astronomisches Institut der Universität Basel, Venusstrasse 7, 4102 Binningen, Switzerland
³  School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA

(Received 2 September 2003 / Accepted 6 November 2003)

Abstract
The astrophysical nature of r-process sites is a long-standing mystery and many probable sources have been suggested, among them lower-mass core-collapse supernovae (in the range 8- ), higher-mass core-collapse supernovae (with masses 20  ) and neutron star mergers. In this work, we present a detailed inhomogeneous chemical evolution study that considers for the first time neutron star mergers as major r-process sources, and compare this scenario to the ones in which core-collapse supernovae act as dominant r-process sites. We conclude that, due to the lack of reliable iron and r-process yields as a function of progenitor mass, it is not possible at present to distinguish between the lower-mass and higher-mass supernovae scenarios within the framework of inhomogeneous chemical evolution. However, neutron-star mergers seem to be ruled out as the dominant r-process source, since their low rates of occurrence would lead to r-process enrichment that is not consistent with observations at very low metallicities. Additionally, the considerable injection of r-process material by a single neutron-star merger leads to a scatter in [r-process/Fe] ratios at later times which is much too large compared to observations.

Key words: nuclear reactions, nucleosynthesis, abundances -- stars: abundances -- ISM: abundances -- Galaxy: abundances -- Galaxy: evolution -- Galaxy: halo

Offprint request: D. Argast, argast@quasar.physik.unibas.ch

© ESO 2004

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