Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...279..173b&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 279, no. 1, p. 173-178
Astronomy and Astrophysics
Astrophysics
27
Abundance, Astronomical Models, Explosions, Helium Isotopes, Hydrogen, Lithium Isotopes, Novae, Nuclear Fusion, Beryllium 7, Convection, Convective Flow, Density (Mass/Volume), Hydrodynamics, Mathematical Models
Scientific paper
The possibility of synthesis of Li-7 in explosive hydrogen burning, and particularly in nova conditions, is reinvestigated with the aid of an updated and extended nuclear reaction network. First, a parametrized one-zone explosive nucleosynthesis model is used to delineate qualitatively the explosion timescales and peak temperature-density conditions that are most favorable for the production of Li-7. The predictions of that analysis are confirmed by detailed numerical network calculations. The sensitivity of the Li-7 yields to nuclear reaction rate uncertainties and to the pre-explosion He-3 concentration is also scrutinized. Those parametrized one-zone studies are complemented with Li-7 yield calculations based on the thermodynamic history that detailed hydrodynamic models predict for the base of the accreted layer in nova runaways. It is concluded from all those calculations that the high peak densities that are thought to prevail at the base of the H-burning layer during a nova outburst prevent the built-up of a significant amount of Li-7. The way this conclusion could be modified by the consideration of the convective motions that develop during the nova outburst is analyzed through a parametrized two-zone model. This study shows that the Li-7 yields depend very much on the (still uncertain) mixing time, and can in certain cases indeed be larger than the amounts predicted by one-zone calculations for typical nova conditions. Even so, it appears unlikely that the Li-7 mass fraction in the nova ejecta can exceed largely the solar value for an initial solar He-3 amount. This result, which is at variance with previous predictions and with the nova yields used in recent models for the evolution of the galactic amount of Li-7, remains to be tested by detailed hydrodynamic nova models.
Arnould Marcel
Boffin Henri. M. J.
Mowlavi Nami
Paulus Gerhard G.
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