Fossil Imprints of the First Generation Supernova Ejecta in Extremely Metal-Deficient Stars

Using results of nucleosynthesis calculations for theoretical core-collapse supernova models with various progenitor's masses, it is shown that abundance patterns of C, Mg, Si, Ca, and H seen in extremely metal-deficient stars with [Fe/H] < -2.5 follow those seen in the individual first generation supernova remnants (SNRs). This suggests that most of the stars with [Fe/H] < -2.5 were made from individual supernova (SN) events. To obtain the ratio of heavy elements to hydrogen, a formula is derived to estimate the mass of hydrogen swept up by a SNR when it occurs in the interstellar matter with the primordial abundances. We use [Mg/H] to indicate the metallicities instead of [Fe/H]. The metallicities [Mg/H] predicted from these SNRs range from ~-4 to ~-1.5 and the mass of Mg in a SN is well correlated with its progenitor's mass. Thus the observed [Mg/H] in an extremely metal deficient star has a correspondence to the progenitor's mass. A larger [Mg/H] corresponds to a larger progenitor's mass. Therefore, so called `age-metallicity relation' does not hold for stars with [Fe/H] < -2.5. In contrast, the [Mg/Fe] ratios in the theoretical SNRs have a different trend from those in extremely metal-deficient stars. It is also shown that the observed trend of [Mg/Fe] can predict the Fe yield of each SN given the correspondence of [Mg/H] to the progenitor's mass. The Fe yields thus obtained are consistent with those derived from SN light curve analyses. This indicates that there is still a problem in modelling a core-collapse supernova at its beginning of explosion or mass cut.Comment: 6 pages, 4 figures, 1 table; Accepted for publication in the Astrophysical Journal Letter

Nucleosynthesis in Type II Supernovae

Presupernova evolution and explosive nucleosynthesis in massive stars for main-sequence masses from 13 $M_\odot$ to 70 $M_\odot$ are calculated. We examine the dependence of the supernova yields on the stellar mass, ^{12}C(\alpha, \gamma) ^{16}O} rate, and explosion energy. The supernova yields integrated over the initial mass function are compared with the solar abundances.Comment: 1 Page Latex source, 10 PostScript figures, to appear in Nuclear Physics A, Vol. A616 (1997

Gamma-Ray Lines from Asymmetric Supernovae

We present 3-dimensional SPH simulations of supernova explosions from 100 seconds to 1 year after core-bounce. By extending our modelling efforts to a 3-dimensional hydrodynamics treatment, we are able to investigate the effects of explosion asymmetries on mixing and gamma-ray line emergence in supernovae. A series of initial explosion conditions are implemented, including jet-like and equatorial asymmetries of varying degree. For comparison, symmetric explosion models are also calculated. A series of time slices from the explosion evolution are further analyzed using a 3-dimensional Monte Carlo gamma-ray transport code. The emergent hard X- and gamma-ray spectra are calculated as a function of both viewing angle and time, including trends in the gamma-ray line profiles. We find significant differences in the velocity distribution of radioactive nickel between the symmetric and asymmetric explosion models. The effects of this spatial distribution change are reflected in the overall high energy spectrum, as well as in the individual gamma-ray line profiles.Comment: 32 pages, 14 figures, LAUR-02-6114, http://qso.lanl.gov/~clf "Clumping Asymmetry" section revise

Iron Opacity and the Pulsar of Supernova 1987A

Neutron stars formed in Type II supernovae are likely to be initially obscured by late-time fallback. Although much of the late-time fallback is quickly accreted via neutrino cooling, some material remains on the neutron star, forming an atmosphere which slowly accretes through photon emission. In this paper, we derive structure equations of the fallback atmosphere and present results of one-dimensional simulations of that fallback. The atmosphere remaining after neutrino cooling becomes unimportant (less than the Compton Eddington limit) is only a fraction of the total mass accreted (10^-8 of the accreted mass or 10^-9 solar masses.) Recombined iron dominates the opacity in the outer regions leading to an opacity 1000-10,000 times higher than that of electron scattering alone. The resultant photon emission of the remnant atmosphere is limited to 1/1000th the Compton Eddington Luminosity. The late-time evolution of this system leads to the formation of a photon-driven wind from the accretion of the inner portion of the atmosphere, leaving, for most cases, a bare neutron star on timescales shorter than a year. The degenerate remnant of 1987a may not be a black hole. Instead, the fallback material may have already accreted or blown off in the accretion-driven wind. If the neutron star has either a low magnetic field or a low rotational spin frequency, we would not expect to see the neutron star remnant of 1987a.Comment: 15 pages text + 8 figures, accepted by Ap

Diagnosis of Circumstellar Matter Structure in Type IIn Supernovae with Hydrogen Line Feature

Some supernovae (SNe), such as Type IIn SNe, are powered by collision of the SN ejecta with a dense circumstellar matter (CSM). Their emission spectra show characteristic line shapes of combined broad emission and narrow P-Cyg lines, which should closely relate to the CSM structure and the mass-loss mechanism that creates the dense CSM. We quantitatively investigate the relationship between the line shape and the CSM structure by Monte Carlo radiative transfer simulations, considering two representative cases of dense CSM formed by steady and eruptive mass loss. Comparing the H$\alpha$ emission between the two cases, we find that a narrow P-Cyg line appears in the eruptive case while it does not appear in the steady case, due to the difference in the velocity gradient in the dense CSM. We also reproduce the blue-shifted photon excess observed in some SNe IIn, which is formed by photon transport across the shock wave and find the relationship between the velocity of the shocked matter and the amount of the blue shift of the photon excess. We conclude that the presence or absence of narrow P-Cyg lines can distinguish the mass loss mechanism, and suggest high-resolution spectroscopic observations with $\lambda/ \Delta \lambda \gtrsim 10^4$ after the light curve peak for applying this diagnostic method.Comment: Submitted to Ap