Catalogo Articoli (Spogli Riviste)

OPAC HELP

Titolo:
Full spectrum of turbulence convective mixing II. Lithium production in AGB stars
Autore:
Mazzitelli, I; DAntona, F; Ventura, P;
Indirizzi:
Osservatorio Astron Roma, I-00040 Monte Porzio, Italy Osservatorio Astron Roma Monte Porzio Italy I-00040 Monte Porzio, Italy CNR, Ist Astrofis Spaziale, I-00133 Rome, Italy CNR Rome Italy I-00133CNR, Ist Astrofis Spaziale, I-00133 Rome, Italy
Titolo Testata:
ASTRONOMY AND ASTROPHYSICS
fascicolo: 3, volume: 348, anno: 1999,
pagine: 846 - 860
SICI:
0004-6361(199908)348:3<846:FSOTCM>2.0.ZU;2-D
Fonte:
ISI
Lingua:
ENG
Soggetto:
SOLAR-TYPE STARS; INTERMEDIATE-MASS STARS; SMALL MAGELLANIC CLOUD; GIANT BRANCH STARS; STELLAR EVOLUTION; DEUTERIUM ABUNDANCE; RED GIANTS; S-PROCESS; MODEL; ENVELOPES;
Keywords:
stars : AGB and post-AGB; stars : evolution; stars : mass-loss;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
49
Recensione:
Indirizzi per estratti:
Indirizzo: Ventura, P Osservatorio Astron Roma, I-00040 Monte Porzio, Italy Osservatorio Astron Roma Monte Porzio Italy I-00040 io, Italy
Citazione:
I. Mazzitelli et al., "Full spectrum of turbulence convective mixing II. Lithium production in AGB stars", ASTRON ASTR, 348(3), 1999, pp. 846-860

Abstract

We present results from new, detailed computations of lithium production by hot bottom burning (HBB) in asymptotic,giant branch (AGB) stars of intermediate mass (3.5 less than or equal to M less than or equal to 6M.). The dependence of lithium production on stellar mass, metallicity, mass loss rate, convection and overshooting are discussed. In particular, nuclear burning, turbulent mixing and convective overshooting (if any) are self-consistently coupled by a diffusive algorithm, and the Full Spectrum of Turbulence (FST) model of convection is adopted, with test comparisons to Mixing Length Theory (MLT) stellar models. All the evolutions are followed from pre-main sequence down to late AGE, when stars do not appear any longer lithium rich. A "reference mass" of 6 M., has been chosen since, although relatively close to the upper limit for which degenerate C-12 ignition occurs, all the studied mechanisms show up more clearly. HBB is always found above similar to log L/L. = 4.4, but the range of (initial) masses reaching HBB is largely dependent on convection model, overshooting and metallicity. For solar chemistry, masses greater than or equal to4M. evolve through HBB in the FST case and including core overshooting whereas, with solarly tuned MLT models and no overshooting, only masses greater than or equal to 6M. can reach HBB. These constraints can give feedbacks about the more correct convection model and/or the extent of overshooting, thanks to the signatures of HBB in AGB stars in clusters of known turnoff masses and metallicity. Overshooting (when included) is addressed as an exponentially decreasing diffusion above formally convective regions. It makes convective cores during the main sequence to grow larger, and also starting masses and luminosities in AGB are then larger. However, also preliminary results obtained when allowing displacement of convective elements below convective regions in AGB are shown. In the "reference" case (6M.), we find that overshooting from below the convective envelope totally suppresses thermal pulses and ultimately leads to the formation of massive (similar to 1M.) white dwarfs rich inCarbon and Oxygen immediately below the photosphere.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 29/11/20 alle ore 15:54:29