Studies of evolved stars. V - Nucleosynthesis in hot-bottom convective envelopes

Abstract

view Abstract Citations (157) References (58) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Studies of evolved stars. V. Nucleosynthesis in hot-bottom convective envelopes. Scalo, J. M. ; Despain, K. H. ; Ulrich, R. K. Abstract Convective envelopes fitted to the cores of luminous double shell models have been found to develop high base temperatures, ( ) >c 106 K, during the period between shell flashes. We show that these "hotbottom" envelopes are the result of the increasing influence of radiation pressure on the radiative and adiabatic temperature gradients. Lower limits on the luminosity (Mbol -3.4) and total mass ( l' o) required for the phenomenon are derived; these values depend sensitively on the treatment of the radiative atmosphere and the ionization zones. Light-element nucleosynthesis in hot-bottom envelopes is examined using a convective diffusion model. Large surface 7Li enhancements are produced by the 7Be transport mechanism if the base temperature Tb exceeds 30 x 106 K. Sufficient time before carbon ignition exists for CN processing if Tb > 50 x 106 K, while full CNO processing and hydrogen depletion may occur if Tb > 75 x 106 K. Comparison with observations indicates that nucleosynthesis in hot-bottom envelopes is not the primary cause of the abundance anomalies observed in peculiar red giants, except possibly for the large 13C/12C ratios and lithium enhancements found in some stars. In particular, mixing of triple-a carbon and s-process elements initiated by the helium shell flashes seems to be required in order to satisfy constraints imposed by the observed line and band strengths and luminosities. Subject headings: abundances, stellar - convection - interiors, stellar - late-type stars - nucleosynthesis Publication: The Astrophysical Journal Pub Date: March 1975 DOI: 10.1086/153471 Bibcode: 1975ApJ...196..805S Keywords: Late Stars; Nuclear Fusion; Stellar Evolution; Astronomical Models; Astrophysics; Convection; Giant Stars; Astrophysics full text sources ADS | data products SIMBAD (5) Related Materials (4) Part 1: 1973ApJ...183..151S Part 2: 1973ApJ...184..801S Part 3: 1974ApJ...192..507U Part 4: 1974ApJ...194..361S