3,382 research outputs found
Hypernova Nucleosynthesis and Galactic Chemical Evolution
We study nucleosynthesis in 'hypernovae', i.e., supernovae with very large
explosion energies ( \gsim 10^{52} ergs) for both spherical and aspherical
explosions. The hypernova yields compared to those of ordinary core-collapse
supernovae show the following characteristics: 1) Complete Si-burning takes
place in more extended region, so that the mass ratio between the complete and
incomplete Si burning regions is generally larger in hypernovae than normal
supernovae. As a result, higher energy explosions tend to produce larger [(Zn,
Co)/Fe], small [(Mn, Cr)/Fe], and larger [Fe/O], which could explain the trend
observed in very metal-poor stars. 2) Si-burning takes place in lower density
regions, so that the effects of -rich freezeout is enhanced. Thus
Ca, Ti, and Zn are produced more abundantly than in normal
supernovae. The large [(Ti, Zn)/Fe] ratios observed in very metal poor stars
strongly suggest a significant contribution of hypernovae. 3) Oxygen burning
also takes place in more extended regions for the larger explosion energy. Then
a larger amount of Si, S, Ar, and Ca ("Si") are synthesized, which makes the
"Si"/O ratio larger. The abundance pattern of the starburst galaxy M82 may be
attributed to hypernova explosions. Asphericity in the explosions strengthens
the nucleosynthesis properties of hypernovae except for "Si"/O. We thus suggest
that hypernovae make important contribution to the early Galactic (and cosmic)
chemical evolution.Comment: To be published in "The Influence of Binaries on Stellar Population
Studies", ed. D. Vanbeveren (Kluwer), 200
The Peculiar Type Ic Supernova 1997ef: Another Hypernova
SN 1997ef has been recognized as a peculiar supernova from its light curve
and spectral properties. The object was classified as a Type Ic supernova (SN
Ic) because its spectra are dominated by broad absorption lines of oxygen and
iron, lacking any clear signs of hydrogen or helium line features. The light
curve is very different from that of previously known SNe Ic, showing a very
broad peak and a slow tail. The strikingly broad line features in the spectra
of SN 1997ef, which were also seen in the hypernova SN 1998bw, suggest the
interesting possibility that SN 1997ef may also be a hypernova. The light curve
and spectra of SN 1997ef were modeled first with a standard SN~Ic model
assuming an ordinary kinetic energy of explosion erg. The
explosion of a CO star of mass gives a
reasonably good fit to the light curve but clearly fails to reproduce the broad
spectral features. Then, models with larger masses and energies were explored.
Both the light curve and the spectra of SN 1997ef are much better reproduced by
a C+O star model with 8 \e{51} erg and .
Therefore, we conclude that SN 1997ef is very likely a hypernova on the basis
of its kinetic energy of explosion. Finally, implications for the deviation
from spherical symmetry are discussed in an effort to improve the light curve
and spectral fits.Comment: "To appear in the Astrophysical Journal, Vol.534 (2000)
Supernova Hosts for Gamma-Ray Burst Jets: Dynamical Constraints
I constrain a possible supernova origin for gamma-ray bursts by modeling the
dynamical interaction between a relativistic jet and a stellar envelope
surrounding it. The delay in observer's time introduced by the jet traversing
the envelope should not be long compared to the duration of gamma-ray emission;
also, the jet should not be swallowed by a spherical explosion it powers. The
only stellar progenitors that comfortably satisfy these constraints, if one
assumes that jets move ballistically within their host stars, are compact
carbon-oxygen or helium post-Wolf-Rayet stars (type Ic or Ib supernovae); type
II supernovae are ruled out. Notably, very massive stars do not appear capable
of producing the observed bursts at any redshift unless the stellar envelope is
stripped prior to collapse. The presence of a dense stellar wind places an
upper limit on the Lorentz factor of the jet in the internal shock model;
however, this constraint may be evaded if the wind is swept forward by a photon
precursor. Shock breakout and cocoon blowout are considered individually;
neither presents a likely source of precursors for cosmological GRBs.
These envelope constraints could conceivably be circumvented if jets are
laterally pressure-confined while traversing the outer stellar envelope. If so,
jets responsible for observed GRBs must either have been launched from a region
several hundred kilometers wide, or have mixed with envelope material as they
travel. A phase of pressure confinement and mixing would imprint correlations
among jets that may explain observed GRB variability-luminosity and
lag-luminosity correlations.Comment: 17 pages, MNRAS, accepted. Contains new analysis of pressure-confined
jets, of jets that experience oblique shocks or mix with their cocoons, and
of cocoons after breakou
Thermal Evolution and Light Curves of Young Bare Strange Stars
The cooling of a young bare strange star is studied numerically by solving
the equations of energy conservation and heat transport for both normal and
superconducting strange quark matter inside the star. We show that the thermal
luminosity from the strange star surface, due to both photon emission and e+e-
pair production, may be orders of magnitude higher than the Eddington limit,
for about one day for normal quark matter but possibly for up to a hundred
years for superconducting quark matter, while the maximum of the photon
spectrum is in hard X-rays with a mean energy of ~ 100 keV or even more. This
differs both qualitatively and quantitatively from the photon emission from
young neutron stars and provides a definite observational signature for bare
strange stars. It is shown that the energy gap of superconducting strange quark
matter may be estimated from the light curves if it is in the range from ~ 0.5
MeV to a few MeV.Comment: Ref [10] added and abstract shortened. 4 pages, 3 figures, revtex4.
To be published in Phys. Rev. Letter
Plasmons in coupled bilayer structures
We calculate the collective charge density excitation dispersion and spectral
weight in bilayer semiconductor structures {\it including effects of interlayer
tunneling}. The out-of-phase plasmon mode (the ``acoustic'' plasmon) develops a
long wavelength gap in the presence of tunneling with the gap being
proportional to the square root (linear power) of the tunneling amplitude in
the weak (strong) tunneling limit. The in-phase plasmon mode is qualitatively
unaffected by tunneling. The predicted plasmon gap should be a useful tool for
studying many-body effects.Comment: 10 pages, 6 figures. to appear in Phys. Rev. Let
Excitation of Giant Monopole Resonance in Pb and Sn Using Inelastic Deuteron Scattering
The excitation of the isoscalar giant monopole resonance (ISGMR) in
Sn and Pb has been investigated using small-angle (including
) inelastic scattering of 100 MeV/u deuteron and
multipole-decomposition analysis (MDA). The extracted strength distributions
agree well with those from inelastic scattering of 100 MeV/u
particles. These measurements establish deuteron inelastic scattering at E 100 MeV/u as a suitable probe for extraction of the ISGMR strength with
MDA, making feasible the investigation of this resonance in radioactive
isotopes in inverse kinematics.Comment: 5 pages, 4 figures. To be published in Phys. Lett.
A flattening in the Optical Light Curve of SN 2002ap
We present the broad band optical photometry of the Type Ic
supernova SN 2002ap obtained during 2002 February 06 -- March 23 in the early
decline phases and also later on 2002 15 August. Combining these data with the
published ones, the general light curve development is studied. The time and
luminosity of the peak brightness and the peak width are estimated. There is a
flattening in the optical light curve about 30 days after the maximum. The
flux decline rates before flattening are 0.1270.005, 0.0820.001,
0.0740.001, 0.0620.001 and 0.0400.001 mag day in ,
, , and passbands respectively, while the corresponding
values after flattening are about 0.02 mag day in all the passbands. The
maximum brightness of SN 2002ap mag, is comparable to that of
the type Ic 1997ef, but fainter than that of the type Ic hypernova SN 1998bw.
The peak luminosity indicates an ejection of 0.06 M
Ni mass.
We also present low-resolution optical spectra obtained during the early
phases.
The SiII absorption minimum indicates that the photospheric velocity
decreased from
21,360 km s to 10,740 km s during a period of 6
days.Comment: 7 pages, 5 figures, Submitted to MNRA
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