10 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
Gamma Ray Lines from the Orion Complex
We show that the 4.44 and 6.13 MeV line emission observed with COMPTEL from
Orion is consistent with gamma ray spectra consisting of a mixture of narrow
and broad lines or spectra containing only broad lines. We employed several
accelerated particle compositions and showed that the current COMPTEL data in
the 3--7 MeV region alone cannot distinguish between the various possibilities.
However, the COMPTEL upper limits in the 1--3 MeV band favor a composition
similar to that of the winds of Wolf-Rayet stars of spectral type WC. The power
dissipated by the accelerated particles at Orion is about 4 10
erg s. These particles are not expected to produce significant amounts
of Al.Comment: 12 pages, uuencoded compressed postscript with 4 figures ApJL in
press 199
Lithium-6 from Solar Flares
By introducing a hitherto ignored Li-6 producing process, due to accelerated
He-3 reactions with He-4, we show that accelerated particle interactions in
solar flares produce much more Li-6 than Li-7. By normalizing our calculations
to gamma-ray data we demonstrate that the Li-6 produced in solar flares,
combined with photospheric Li-7, can account for the recently determined solar
wind lithium isotopic ratio, obtained from measurements in lunar soil, provided
that the bulk of the flare produced lithium is evacuated by the solar wind.
Further research in this area could provide unique information on a variety of
problems, including solar atmospheric transport and mixing, solar convection
and the lithium depletion issue, and solar wind and solar particle
acceleration.Comment: latex 9 pages, 2 figures, ApJ Letters in pres
Light Element Evolution and Cosmic Ray Energetics
Using cosmic-ray energetics as a discriminator, we investigate evolutionary
models of LiBeB. We employ a Monte Carlo code which incorporates the delayed
mixing into the ISM both of the synthesized Fe, due to its incorporation into
high velocity dust grains, and of the cosmic-ray produced LiBeB, due to the
transport of the cosmic rays. We normalize the LiBeB production to the integral
energy imparted to cosmic rays per supernova. Models in which the cosmic rays
are accelerated mainly out of the average ISM significantly under predict the
measured Be abundance of the early Galaxy, the increase in [O/Fe] with
decreasing [Fe/H] notwithstanding. We suggest that this increase could be due
to the delayed mixing of the Fe. But, if the cosmic-ray metals are accelerated
out of supernova ejecta enriched superbubbles, the measured Be abundances are
consistent with a cosmic-ray acceleration efficiency that is in very good
agreement with the current epoch data. We also find that neither the above
cosmic-ray origin models nor a model employing low energy cosmic rays
originating from the supernovae of only very massive progenitors can account
for the Li data at values of [Fe/H] below 2.Comment: latex 19 pages, 2 tables, 10 eps figures, uses aastex.cls natbib.sty
Submitted to the Astrophysical Journa
X-Rays from Accelerated Ion Interactions
We have developed in detail the theory of X-ray line and continuum production
due to atomic interactions of accelerated ions, incorporating in our
calculations information from a broad range of laboratory measurements. We
applied our calculations to the Orion region from which nuclear gamma-ray lines
were observed with the COMPTEL instrument on CGRO. The accelerated particles
which produce this gamma-ray emission via nuclear reactions also produce X-ray
lines via atomic interactions. We predict strong line emission in the range
from 0.5 to 1 keV, mainly due to de-excitations in fast O ions. While much of
the diffuse X-ray emission observed with ROSAT from Orion could be due to
accelerated ions, the current X-ray data do not provide unambiguous signatures
for such an origin. If future observations with high spectral resolution would
confirm the predicted X-rays, the combined analysis of the X-ray and gamma-ray
data will set important constraints on the origin of the accelerated particles
and their interaction model.Comment: 26 pages, 14 figure
High-resolution observation of the solar positron-electron annihilation line, Astrophys
ABSTRACT The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) has observed the positron-electron annihilation line at 511 keV produced during the 2002 July 23 solar flare. The shape of the line is consistent with annihilation in two vastly different solar environments. It can be produced by formation of positronium by charge exchange in flight with hydrogen in a quiet solar atmosphere at a temperature of ∼6000 K. However, the measured upper limit to the ratio (ratio of annihilation photons in the positronium continuum to the number 3g/2g in the line) is only marginally consistent with what is calculated for this environment. The annihilation line can also be fitted by a thermal Gaussian having a width of keV (FWHM), indicating temperatures of 8.1 ‫ע‬ 1.1 ∼ K. The measured ratio does not constrain the density when the annihilation takes place in 5 (4-7) # 10 3g/2g such an ionized medium, although the density must be high enough to slow down the positrons. This would require the formation of a substantial mass of atmosphere at transition-region temperatures during the flare