SYSTEMATICS OF DYNAMICAL MASS EJECTION, NUCLEOSYNTHESIS, AND RADIOACTIVELY POWERED ELECTROMAGNETIC SIGNALS FROM NEUTRON-STAR MERGERS

We investigate systematically the dynamical mass ejection, r-process nucleosynthesis, and properties of electromagnetic counterparts of neutron-star (NS) mergers in dependence on the uncertain properties of the nuclear equation of state (EOS) by employing 40 representative, microphysical high-density EOSs in relativistic, hydrodynamical simulations. The crucial parameter determining the ejecta mass is the radius R-1.35 of a 1.35 M-circle dot NS. NSs with smaller R1.35 (soft EOS) eject systematically higher masses. These range from similar to 10(-3) M-circle dot to similar to 10(-2) M-circle dot for 1.35-1.35 M-circle dot binaries and from similar to 5 x 10(-3) M-circle dot to similar to 2 x 10(-2) M-circle dot for 1.2-1.5 M-circle dot systems (with kinetic energies between similar to 5 x 10(49) erg and 10(51) erg). Correspondingly, the bolometric peak luminosities of the optical transients of symmetric (asymmetric) mergers vary between 3 x 10(41) erg s(-1) and 14 x 10(41) erg s(-1) (9 x 10(41) erg s(-1) and 14.5x10(41) erg s(-1)) on timescales between similar to 2 hr and similar to 12 hr. If these signals with absolute bolometric magnitudes from -15.0 to -16.7 are measured, the tight correlation of their properties with those of the merging NSs might provide valuable constraints on the high-density EOS. The r-process nucleosynthesis exhibits a remarkable robustness independent of the EOS, producing a nearly solar abundance pattern above mass number 130. By the r-process content of the Galaxy and the average production per event the Galactic merger rate is limited to 4 x 10(-5) yr(-1) (4x10(-4) yr(-1)) for a soft (stiff) NS EOS, if NS mergers are the main source of heavy r-nuclei. The production ratio of radioactive Th-232 to U-238 attains a stable value of 1.64-1.67, which does not exclude NS mergers as potential sources of heavy r-material in the most metal-poor stars.