220 research outputs found
Synthesis of 4th order lossy filters with uniform Q distribution
Postprint (published version
Comparison of lossy filters and predistorted filters using novel software
Postprint (published version
The Imprint of Nova Nucleosynthesis in Presolar Grains
Infrared and ultraviolet observations of nova light curves have confirmed
grain formation in their expanding shells that are ejected into the
interstellar medium by a thermonuclear runaway. In this paper, we present
isotopic ratios of intermediate-mass elements up to silicon for the ejecta of
CO and ONe novae, based on 20 hydrodynamic models of nova explosions. These
theoretical estimates will help to properly identify nova grains in primitive
meteorites. In addition, equilibrium condensation calculations are used to
predict the types of grains that can be expected in the nova ejecta, providing
some hints on the puzzling formation of C-rich dust in O>C environments. These
results show that SiC grains can condense in ONe novae, in concert with an
inferred (ONe) nova origin for several presolar SiC grains.Comment: 42 pages. Accepted for publication in The Astrophysical Journa
Presolar Grains from Novae
We report the discovery of five SiC grains and one graphite grain isolated
from the Murchison carbonaceous meteorite whose major-element isotopic
compositions indicate an origin in nova explosions. The grains are
characterized by low 12C/13C (4-9) and 14N/15N (5-20) ratios, large excesses in
30Si (30Si/28Si ratios range to 2.1 times solar) and high 26Al/27Al ratios.
These isotopic signatures are theoretically predicted for the ejecta from ONe
novae and cannot be matched by any other stellar sources. Previous studies of
presolar grains from primitive meteorites have shown that the vast majority
formed in red giant outflows and supernova ejecta. Although a classical nova
origin was suggested for a few presolar graphite grains on the basis of 22Ne
enrichments, this identification is somewhat ambiguous since it is based only
on one trace element. Our present study presents the first evidence for nova
grains on the basis of major element isotopic compositions of single grains. We
also present the results of nucleosynthetic calculations of classical nova
models and compare the predicted isotopic ratios with those of the grains. The
comparison points toward massive ONe novae if the ejecta are mixed with
material of close-to-solar composition.Comment: 20 pages, 5 figures, 1 table. ApJ, in pres
Catching Element Formation In The Act
Gamma-ray astronomy explores the most energetic photons in nature to address
some of the most pressing puzzles in contemporary astrophysics. It encompasses
a wide range of objects and phenomena: stars, supernovae, novae, neutron stars,
stellar-mass black holes, nucleosynthesis, the interstellar medium, cosmic rays
and relativistic-particle acceleration, and the evolution of galaxies. MeV
gamma-rays provide a unique probe of nuclear processes in astronomy, directly
measuring radioactive decay, nuclear de-excitation, and positron annihilation.
The substantial information carried by gamma-ray photons allows us to see
deeper into these objects, the bulk of the power is often emitted at gamma-ray
energies, and radioactivity provides a natural physical clock that adds unique
information. New science will be driven by time-domain population studies at
gamma-ray energies. This science is enabled by next-generation gamma-ray
instruments with one to two orders of magnitude better sensitivity, larger sky
coverage, and faster cadence than all previous gamma-ray instruments. This
transformative capability permits: (a) the accurate identification of the
gamma-ray emitting objects and correlations with observations taken at other
wavelengths and with other messengers; (b) construction of new gamma-ray maps
of the Milky Way and other nearby galaxies where extended regions are
distinguished from point sources; and (c) considerable serendipitous science of
scarce events -- nearby neutron star mergers, for example. Advances in
technology push the performance of new gamma-ray instruments to address a wide
set of astrophysical questions.Comment: 14 pages including 3 figure
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