The Yields of r-Process Elements and Chemical Evolution of the Galaxy

The supernova yields of r-process elements are obtained as a function of the mass of their progenitor stars from the abundance patterns of extremely metal-poor stars on the left-side [{Ba/Mg}]--[{Mg/H}] boundary with a procedure proposed by Tsujimoto and Shigeyama. The ejected masses of r-process elements associated with stars of progenitor mass M_ms ≤ 18 M_⊙ are infertile sources and the SNe II with 20 M_⊙ ≤ M_ms ≤ 40 M_⊙ are the dominant source of r-process nucleosynthesis in the Galaxy. The ratio of these stars 20 M_⊙ ≤ M_ms ≤ 40 M_⊙with compared to the all massive stars is about∼ 18%. In this paper, we present a simple model that describes a star's [r/Fe] in terms of the nucleosynthesis yields of r-process elements and the number of SN II explosions. Combined the r-process yields obtained by our procedure with the scatter model of the Galactic halo, the observed abundance patterns of the metal-poor stars can be well reproduced.