On the formation and evolution of super-asymptotic giant branch stars with cores processed by carbon burning. 1: SPICA to Antares

Abstract

view Abstract Citations (104) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Formation and Evolution of Super--Asymptotic Giant Branch Stars with Cores Processed by Carbon Burning. I. SPICA to Antares Garcia-Berro, Enrique ; Iben, I. Abstract A 10 solar mass model of Population I composition is evolved from the hydrogen-burning main sequence onto the early 'super'-asymptotic giant branch (ESAGB), where hydrogen does not burn, the dominant source of surface luminosity is shell helium burning, and carbon burning in the helium-exhausted core converts all of the initial C-12 and Ne-22 and some of the O-16 in this core into isotopes of oxygen, neon, sodium, magnesium, and other heavy elements. The entire ESAGB phase lasts approximately 4.6 x 104 yr, and helium burning is the primary source of surface luminosity for all but approximately 3000 yr. The carbon-burning phase lasts approximately 2 x 104 yr. In comparison, the main-sequence phase lasts approximately 2 x 107 yr, and the core helium-burning phase lasts approximately 4 x 106 yr. At the end of the core carbon-burning phase, dredge-up decreases the mass of the hydrogen-exhausted core from approximately 2.46 solar mass to approximately 1.315 solar mass. During the dredge-up episode, in addition to products of complete hydrogen burning, products of incomplete helium burning are mixed into the hydrogen-rich convective enevelope. At the end of the second dredge-up phase, the model has an electron-degenerate carbon-exhausted core of mass approximately 1.285 solar mass. Between the carbon-exhausted core and the hydrogen-rich convective envelope are three layers which are each of mass approximately 0.01 solar mass and which contain (1) C-12 and O-16 at comparable abundances by mass; (2) C-12 and He-4 at comparable abundances by mass; and (3) mostly He-4 with some C-12. The abundances by mass of the main constituents of the carbon-exhausted core vary signifcantly through the core. At the center, abundances of mass are X(O-16) approximately 0.80, X(Ne-20) approximately 0.11, X(Na-22) approximately 0.03, X(Mg-24) approximatelly 0.0075, and X(Mg-26) approximately 0.01, whereas, near the edge of the core, X(O-16) approximately 0.19, X(Ne-20) approximately 0.50, X(Na-23) approximately 0.04, and X(Mg-24) approximately 0.27. The abundance of Na-23 is large enough that, if the mass of the SAGB core can grow to approximately 1.37 solar mass, core collapse into a neutron star will be initiated by electron capture on Na-23 rather than on Mg-24. Publication: The Astrophysical Journal Pub Date: October 1994 DOI: 10.1086/174729 Bibcode: 1994ApJ...434..306G Keywords: Asymptotic Giant Branch Stars; Carbon; Helium; Nuclear Fusion; Star Formation; Stellar Composition; Stellar Cores; Stellar Evolution; Stellar Models; Abundance; Main Sequence Stars; Red Giant Stars; Stellar Luminosity; Astrophysics; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; ABUNDANCES; STARS: AGB AND POST-AGB; STARS: EVOLUTION; STARS: INTERIORS; STARS: SUPERGIANTS full text sources ADS | data products SIMBAD (2) Related Materials (4) Part 2: 1996ApJ...460..489R Part 3: 1997ApJ...485..765G Part 4: 1997ApJ...489..772I Part 5: 1999ApJ...515..381R