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Titolo:
EVOLUTION AND NUCLEOSYNTHESIS IN LOW-MASS ASYMPTOTIC GIANT BRANCH STARS .1. FORMATION OF POPULATION-I CARBON STARS
Autore:
STRANIERO O; CHIEFFI A; LIMONGI M; BUSSO M; GALLINO R; ARLANDINI C;
Indirizzi:
OSSERVATORIO ASTRON COLLURANIA TERAMO ITALY CNR,IST ASTROFIS SPAZIALE I-00044 FRASCATI ITALY OSSERV ASTRON ROMA I-00136 ROME ITALY OSSERV ASTRON TORINO TURIN ITALY UNIV TURIN,DIPARTIMENTO FIS GEN TURIN ITALY
Titolo Testata:
The Astrophysical journal
fascicolo: 1, volume: 478, anno: 1997,
parte:, 1
pagine: 332 - 339
SICI:
0004-637X(1997)478:1<332:EANILA>2.0.ZU;2-9
Fonte:
ISI
Lingua:
ENG
Soggetto:
CHEMICAL-COMPOSITION; STELLAR MODELS; RED GIANTS;
Keywords:
NUCLEAR REACTIONS, NUCLEOSYNTHESIS, ABUNDANCES; STARS, AGB AND POST-AGB; STARS, CARBON; STARS, EVOLUTION; STARS, INTERIORS;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
35
Recensione:
Indirizzi per estratti:
Citazione:
O. Straniero et al., "EVOLUTION AND NUCLEOSYNTHESIS IN LOW-MASS ASYMPTOTIC GIANT BRANCH STARS .1. FORMATION OF POPULATION-I CARBON STARS", The Astrophysical journal, 478(1), 1997, pp. 332-339

Abstract

New models of thermally pulsing asymptotic giant branch (TP-AGB) stars of low mass and solar chemical composition are presented, namely, 1 less than or equal to M/M. less than or equal to 3, Z = 0.02, and Y = 0.28, The iufluence of various parameters (such as the initial core mass, the envelope mass, the mass-loss rate, the opacity, and the mixinglength) on the properties of the models is discussed in detail. Our main findings are the following: 1. The third dredge-up (TDU) operates self-consistently (using the Schwarzschild criterion for convection and without invoking any extra-mixing) for masses as low as 1.5 M.. The minimum core mass for which TDU is found is M(H) similar to 0.61 M.. This value is attained after about 10 thermal pulses, almost independently of the initial mass. 2. During the early TP-AGB evolution, the relation between the pulse strength (i.e., the luminosity peak of the 3 alpha burning during the pulse) and the core mass is in good agreement with previous findings. However, when TDU is settled on, the strength of the pulse increases more rapidly as the penetration of the convective envelope into the He intershell increases. No asymptotic limit is found. 3. Furthermore, the 3 alpha luminosity peak is independent of the previous history: the strength of the pulse in a model with mass loss is the same as in a model without mass loss but having the same coreand envelope masses. 4. Unless extreme mass-loss rates are assumed, carbon stars are obtained in all the sequences of models with initial mass M greater than or equal to 1.5 M. after about 24-26 thermal pulsesand 15-17 TDU episodes. At C-star formation, the core mass is less than 0.7 M., and the luminosity is of the order of 10(4) L. dredged-up mass increases up to a maximum and then decreases as mass loss and/or the advancement of the H-burning shell consume the envelope. When the envelope mass is reduced below approximately 0.5 M., TDU eventually vanishes. 5. If some amount of protons is diffused below the base of the H-rich envelope during TDU, in the interpulse a C-13-pocket is formed and then burnt radiatively via the C-13(alpha, n)O-16 reaction, beforethe onset of a new pulse. Thus, s-process nucleosynthesis occurs in aradiative environment characterized by a fairly low neutron density. In advanced thermal pulses, when the temperature at the bottom of the convective shell approaches 3 x 10(8) K, a secondary source of neutrons comes from the marginal activation of the Ne-22(alpha, n)Mg-25 reaction.

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Documento generato il 04/12/20 alle ore 13:09:38