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 $>$30 MeV/nucl); and only 10$^{49}$ 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$^5$ years ago based on the age of the Geminga pulsar). The unequivocal signature of lines from deexcitations in fast ions is their large width ($\delta E/E$~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