28 research outputs found
Light Elements and Cosmic Rays in the Early Galaxy
We derive constraints on the cosmic rays responsible for the Be and part of
the B observed in stars formed in the early Galaxy: the cosmic rays cannot be
accelerated from the ISM; their energy spectrum must be relatively hard (the
bulk of the nuclear reactions should occur at 30 MeV/nucl); and only
10 erg/SNII in high metallicity, accelerated particle kinetic energy
could suffice to produce the Be and B. The reverse SNII shock could accelerate
the particles.Comment: 5 pages LATEX using paspconf.sty file with one embedded eps figure
using psfig. In press, Proc. Goddard High Resolution Spectrograph Symposium,
PASP, 199
Diffuse 0.5-1 keV X-Rays and Nuclear Gamma-Rays from Fast Particles in the Local Hot Bubble
We show that interactions of fast particles with the boundary shell of the
local hot bubble could make an important contribution to the 0.5-1 keV diffuse
X-ray background observed with ROSAT. The bulk of these nonthermal X-rays are
due to line emission from fast O ions of energies around 1 MeV/nucleon. This is
the typical energy per particle in the ejecta of the supernova which is thought
to have energized the bubble. We find that there is sufficient total energy in
the ejecta to produce X-rays of the required intensity, subject to the details
of the evolution of the fast particle population since the supernova explosion
(about 3 10 years ago based on the age of the Geminga pulsar). The
unequivocal signature of lines from deexcitations in fast ions is their large
width (~0.1 for O lines), which will clearly distinguishes them
from X-ray lines produced in a hot plasma. If a small fraction of the total
ejecta energy is converted into accelerated particle kinetic energy (>~30
MeV/nucleon), the gamma-ray line emission produced in the boundary shell of the
local hot bubble could account for the recently reported COMPTEL observations
of nuclear gamma-ray lines from a broad region towards the Galactic center.Comment: 13 pages, 4 figures, submitted to Ap
Nucleosynthesis and Gamma Ray-Line Astronomy
The most energetic part of the electromagnetic spectrum bears the purest
clues to the synthesis of atomic nuclei in the universe. The decay of
radioactive species, synthesized in stellar environments and ejected into the
interstellar medium, gives rise to specific gamma ray lines. The observations
gathered up to now show evidence for radioactivities throughout the galactic
disk, in young supernova remnants (Cas A, Vela), and in nearby extragalactic
supernovae (SN 1987A, SN 1991T and SN1998bu), in the form of specific gamma ray
lines resulting, respectively, from the radioactive decay of 26Al, 44Ti and
56Co. The various astrophysical sites of thermal nucleosynthesis of the
radioactive nuclei were discussed: AGB and Wolf-Rayet stars, novae, and type Ia
and type II supernovae. Nuclear excitations by fast particles also produce
gamma ray lines which have been observed in great detail from solar flares, and
more hypothetically from active star forming regions where massive supernovae
and WR stars abound. This non thermal process and its nucleosynthetic
consequences was reviewed. The 511 keV line arising from e+ + e- annihilation
also provides important information on explosive nucleosynthesis, as well as on
the nature of the interstellar medium where the positrons annihilate. INTEGRAL,
the main mission devoted to high resolution nuclear spectroscopy, should lead
to important progress in this field.Comment: 4 page