6,339 research outputs found
Evidence Against an Association Between Gamma-Ray Bursts and Type I Supernovae
We present a rigorous method, based on Bayesian inference, for calculating
the odds favoring the hypothesis that any particular class of astronomical
transients produce gamma-ray bursts over the hypothesis that they do not. We
then apply this method to a sample of 83 Type Ia supernovae and a sample of 20
Type Ib-Ic supernovae. We find overwhelming odds against the hypothesis that
all Type Ia supernovae produce gamma-ray bursts, whether at low redshift
() or high-redshift (), and very large odds ()
against the hypothesis that all Type Ib, Ib/c, and Ic supernovae produce
observable gamma-ray bursts. We find large odds () against the hypothesis
that a fraction of Type Ia supernovae produce observable gamma-ray bursts, and
moderate odds () against the hypothesis that a fraction of Type Ib-Ic
supernovae produce observable bursts. We have also re-analyzed both a corrected
version of the Wang & Wheeler sample of Type Ib-Ic SNe and our larger sample of
20 Type Ib-Ic SNe, using a generalization of their frequentist method. We find
no significant evidence in either case of a correlation between Type Ib-Ic SNe
and GRBs, consistent with the very strong evidence against such a correlation
that we find from our Bayesian analysis.Comment: 45 pages, 2 PostScript figures. Uses AASTEX macros. Submitted to The
Astrophysical Journa
Process for controlling morphology and improving thermal-mechanical performance of high performance interpenetrating and semi-interpenetrating polymer networks
In the process of the present invention, a non-polar, aprotic solvent is removed from an oligomer/polymer solution by freeze-drying in order to produce IPNs and semi-IPNs. By thermally quenching the solution to a solid in a short length of time, the size of the minor constituent-rich regions is greatly reduced as they are excluded along with the major constituent from the regions of crystallizing solvent. The use of this process sequence of controlling phase morphology provides IPNs and semi-IPNs with improved fracture toughness, microcracking resistance, and other physical-mechanical properties as compared to IPNs and semi-IPNs formed when the solvent is evaporated rather than sublimed
Feshbach resonances in Cesium at Ultra-low Static Magnetic Fields
We have observed Feshbach resonances for 133Cs atoms in two different
hyperfine states at ultra-low static magnetic fields by using an atomic
fountain clock. The extreme sensitivity of our setup allows for high
signal-to-noise-ratio observations at densities of only 2*10^7 cm^{-3}. We have
reproduced these resonances using coupled-channels calculations which are in
excellent agreement with our measurements. We justify that these are s-wave
resonances involving weakly-bound states of the triplet molecular Hamiltonian,
identify the resonant closed channels, and explain the observed multi-peak
structure. We also describe a model which precisely accounts for the
collisional processes in the fountain and which explains the asymmetric shape
of the observed Feshbach resonances in the regime where the kinetic energy
dominates over the coupling strength.Comment: 5 pages, 4 figures, 1 tabl
Measuring ^{12}C(&alpha,&gamma)^{16}O from White Dwarf Asteroseismology
During helium burning in the core of a red giant, the relative rates of the
3&alpha and ^{12}C(&alpha,&gamma)^{16}O reactions largely determine the final
ratio of carbon to oxygen in the resulting white dwarf star. The uncertainty in
the 3&alpha reaction at stellar energies due to the extrapolation from
high-energy laboratory measurements is relatively small, but this is not the
case for the ^{12}C(&alpha,&gamma)^{16}O reaction. Recent advances in the
analysis of asteroseismological data on pulsating white dwarf stars now make it
possible to obtain precise measurements of the central ratio of carbon to
oxygen, providing a more direct way to measure the ^{12}C(&alpha,&gamma)^{16}O
reaction rate at stellar energies. We assess the systematic uncertainties of
this approach and quantify small shifts in the measured central oxygen
abundance originating from the observations and from model settings that are
kept fixed during the optimization. Using new calculations of white dwarf
internal chemical profiles, we find a rate for the ^{12}C(&alpha,&gamma)^{16}O
reaction that is significantly higher than most published values. The accuracy
of this method may improve as we modify some of the details of our description
of white dwarf interiors that were not accessible through previous
model-fitting methods.Comment: 8 pages, 4 figures, 3 tables, uses emulateapj5.sty, Accepted for
publication in the Astrophysical Journa
Near-IR studies of recurrent nova V745 Scorpii during its 2014 outburst
The recurrent nova (RN) V745 Scorpii underwent its third known outburst on
2014 February 6. Infrared monitoring of the eruption on an almost daily basis,
starting from 1.3d after discovery, shows the emergence of a powerful blast
wave generated by the high velocity nova ejecta exceeding 4000 kms
plowing into its surrounding environment. The temperature of the shocked gas is
raised to a high value exceeding 10K immediately after outburst
commencement. The energetics of the outburst clearly surpass those of similar
symbiotic systems like RS Oph and V407 Cyg which have giant secondaries. The
shock does not show a free-expansion stage but rather shows a decelerative
Sedov-Taylor phase from the beginning. Such strong shockfronts are known to be
sites for ray generation. V745 Sco is the latest nova, apart from five
other known novae, to show ray emission. It may be an important
testbed to resolve the crucial question whether all novae are generically
ray emitters by virtue of having a circumbinary reservoir of material
that is shocked by the ejecta rather than ray generation being
restricted to only symbiotic systems with a shocked red giant (RG) wind. The
lack of a free-expansion stage favors V745 Sco to have a density enhancement
around the white dwarf (WD), above that contributed by a RG wind. Our analysis
also suggests that the WD in V745 Sco is very massive and a potential
progenitor for a future SN Ia explosion.Comment: To appear in ApJ (Letters
A New Sub-Period-Minimum Cataclysmic Variable With Partial Hydrogen Depletion And Evidence Of Spiral Disk Structure
We present time-resolved spectroscopy and photometry of CSS 120422:111127+571239 (=SBS 1108+574), a recently discovered SU UMa-type dwarf nova whose 55 minute orbital period is well below the cataclysmic variable (CV) period minimum of similar to 78 minutes. In contrast with most other known CVs, its spectrum features He I emission of comparable strength to the Balmer lines, implying a hydrogen abundance less than 0.1 of long-period CVs-but still at least 10 times higher than that in AM CVn stars. Together, the short orbital period and remarkable helium-to-hydrogen ratio suggest that mass transfer in CSS 120422 began near the end of the donor star's main-sequence lifetime, meaning that this CV is a strong candidate progenitor of an AM CVn system as described by Podsiadlowski et al. Moreover, a Doppler tomogram of the Ha line reveals two distinct regions of enhanced emission. While one is the result of the stream-disk impact, the other is probably attributable to spiral disk structure generated when material in the outer disk achieves a 2:1 orbital resonance with respect to the donor.NSF AST-1211196, AST-9987045Department of Physics at the University of Notre DameNSF Telescope System Instrumentation Program (TSIP)Ohio Board of RegentsOhio State University Office of ResearchAstronom
Near-infrared line identification in type Ia supernovae during the transitional phase
We present near-infrared synthetic spectra of a delayed-detonation
hydrodynamical model and compare them to observed spectra of four normal type
Ia supernovae ranging from day +56.5 to day +85. This is the epoch during which
supernovae are believed to be undergoing the transition from the photospheric
phase, where spectra are characterized by line scattering above an optically
thick photosphere, to the nebular phase, where spectra consist of optically
thin emission from forbidden lines. We find that most spectral features in the
near-infrared can be accounted for by permitted lines of Fe II and Co II. In
addition, we find that [Ni II] fits the emission feature near 1.98 {\mu}m,
suggesting that a substantial mass of 58Ni exists near the center of the ejecta
in these objects, arising from nuclear burning at high density. A tentative
identification of Mn II at 1.15 {\mu}m may support this conclusion as well.Comment: accepted to Ap
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