Osamu Koike

p-process nucleosynthesis inside supernova-driven supercritical accretion disks

We investigate p-process nucleosynthesis in a supercritical accretion disk around a compact object of 1.4 M☉, using the self-similar solution of an optically thick advection-dominated flow. Supercritical accretion is expected to occur in a supernova with fallback material accreting onto a newborn compact object. It is found that an appreciable number of p-nuclei are synthesized via the p-process in supernova-driven supercritical accretion disks (SSADs) when the accretion rate = c2/(16LEdd) > 105, where LEdd is the Eddington luminosity. Abundance profiles of p-nuclei ejected from SSADs have features similar to those of the oxygen/neon layers in Type II supernovae when the abundance of the fallback gas far from the compact object is that of the oxygen/neon layers in the progenitor. The overall abundance profile is in agreement with that of the solar system. Some p-nuclei, such as Mo, Ru, Sn, and La, are underproduced in the SSADs as in Type II supernovae. If the fallback gas is mixed with a small fraction of protons through Rayleigh-Taylor instability during the explosion, significant amounts of 92Mo are produced inside the SSADs. Isotopes 96Ru and 138La are also produced when the fallback gas contains abundant protons, although the overall abundance profile of p-nuclei is rather different from that of the solar system. The p-process nucleosynthesis in SSADs contributes to the chemical evolution of p-nuclei, in particular 92Mo, if several percent of the fallback matter are ejected via jets and/or winds.

P-process nucleosynthesis inside supernova-driven supercritical accretion disks

Abstract We investigate p-process nucleosynthesis in a supercritical accretion disk around a compact object of 1.4 M ⊙ . Supercritical accretion is expected to occur in a supernova (SN) with fallback material accreting onto a nascent compact object. We find that appreciable amounts of p-nuclei are synthesized via the p-process in the disk when the accretion rate M > 1.6 × 10 6 L Edd c 2 , where L Edd is the Eddington luminosity. Abundance profiles of p-nuclei ejected from SSASs have similar features to those of oxygen/neon layers in the Type II SNe when composition of the fallback gas is initially those of the oxygen/neon layers in the progenitor. The overall abundance profile is in agreement with that of the solar system. Some p-nuclei, such as Mo, Ru, Sn, and La, are underproduced in SSADs as in Type II SNe. If the fallback gas is mixed with a small fraction of proton, significant amounts of 92 Mo and 138 La are produced inside SSADs. 96 Ru, 113 Sn, and 114 Sn are also abundantly produced when the fallback gas contains abundant proton though the overall abundance profile of p-nuclei is rather different from that of the solar system.

Nucleosynthesis inside accretion disks around intermediate-mass black holes

Abstract Nucleosynthesis is investigated inside an accredition disk around a black hole of 50 – 10 3 M ⊙ located in a circumnuclear region of starburst galaxies. Nuclear reactions proceed through the hot CNO cycle to produce large amounts of 14 O and 15 O, which decay to 14 N and 15 N. The calculated N/O − O/H relation is found to be consistent with that observed in the most metal-poor galaxies. The accretion disk may be one of the promising sites of nitrogen production.

Helium flash on accreting neutron stars

Abstract We investigate the helium flash (He-flash) on neutron stars where accreted matter is assumed to be pure helium. Then, we present the results of numerical calculations and compare them with the observation of 4U 1820-30 which is considered the site of the He-flash. Furthermore, we examine the carbon flash (C-flash) with X( 12 C ) = 0.1, which has been proposed to cause superbursts.

Nucleosynthesis of proton rich nuclei on accreting neutron stars related to type I X-ray burst

Abstract Using a shell flash model, we have investigated the relation between the endpoint of the rp-process and the ignition pressure. We have found a striking feature of the rp-process during the burst: nuclear fuel is almost burned out after the flash; the mass number of synthesized nuclei reaches to ∼ 100 for the typical pressure from 10 23 to 10 23.5 [dyn cm −2 ]. These results will severely constrain the model of type I X-ray bursts in reproducing the observational properties such as the shape of the light curve, the total radiated energy and the recurrence time.