Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28r.317a&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 317
Astronomy and Astrophysics
Astrophysics
1
Astrophysics, Extinct Nuclides, Isotopic Anomalies, Nucleosynthesis, Stellar Evolution
Scientific paper
Isotopic anomalies are now known to be carried by high-temperature inclusions of primitive meteorites that formed from solar reservoirs out of equilibrium with the rest of the solar nebula, as well as by various types of grains (diamond, graphite, SiC) that are considered to be of circumstellar origin, and have survived the process of incorporation into the solar system (see e.g. [1] for a recent review). Such anomalies provide new clues to many important astrophysical problems, and raise the question of their nucleosynthetic origin. In fact, they offer the exciting perspective of confronting abundance observations with nucleosynthesis models for a very limited number of events, even possibly a single one. This situation is in marked contrast with the one encountered when trying to understand the bulk solar system composition. Up to now, Red Giant stars, massive mass loosing objects (of the Wolf-Rayet type), novae or supernovae have been proposed as possible contributors to the observed anomalies. In this paper, we revisit the role that could possibly be played in that respect by Wolf-Rayet (WR) stars. Wolf-Rayet stars are appealing isotopic anomaly contributors for many reasons. In particular (1) they are observed to loose mass at very large rates that can exceed 10^-5M solar masses yr^-l, the ejected material being contaminated with the products of hydrogen and helium burning, and (2) certain WR stars are known to make dust episodically in their winds [e.g., 2]. In addition, the role of WR stars would be well in line with the "bing-bang" model for the isotopic anomalies promoted by Reeves [3]. The aim of this contribution is to extent and update previous calculations [4,5] of the isotopic anomalies that could be carried by the wind of WR stars of various masses and initial compositions during different phases of their evolution, those anomalies possibly loading circumstellar WR grains. The calculation of the WR wind composition is performed on grounds of detailed stellar evolutionary models that incorporate extended nuclear reaction networks, as well as recent improvements in our knowledge of various basic physical ingredients, like mass loss rates, opacities, or nuclear reaction rates. Results will be presented for various radionuclides with lifetimes in excess of ~10^5 yr, which are considered to be responsible for certain observed anomalies, or which could lead to anomalies that remain unobserved at present. Isotopic patterns for the elements ranging from carbon to lead will also be presented. Those predictions will be confronted with existing data, or will help unravel cases of potential interest for further laboratory quest. References: [1] Harper C. L. Jr. (1992) In Nuclei in the Cosmos II (F. Kappeler and K. Wisshak, eds.), 113-126, IOP Publ. Co. [2] Williams P. M. et al. (1992) Mon. Not. R. Astron. Soc., 258, 461-475. [3] Reeves H. (1978) In Protostars and Planets (T. Gehrels, ed.), 339-426, Univ. of Arizona. [4] Arnould M. and Prantzos N. (1986) In Nucleosynthesis and Its Implications on Nuclear and Particle Physics, (J. Audouze and N. Mathieu, eds.), 363-372, Reidel. [5] Meynet G. and Arnould M. (1993) In Origin and Evolution of the Elements (N. Prantzos et al., eds.), Cambridge, in press.
Arnould Marcel
Meynet George
Paulus Gerhard G.
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