Hostname: page-component-78c5997874-mlc7c Total loading time: 0 Render date: 2024-11-19T03:25:59.408Z Has data issue: false hasContentIssue false
  • English
  • Français

Fundamental problems and basic tests of stellar evolution theory — The case of carbon stars

Published online by Cambridge University Press:  04 August 2017

Icko Iben Jr.
Icko Iben Jr.*
Affiliation:
University of Illinois at Champaign-Urbana

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

Carbon stars are thought to be in the asymptotic giant branch (AGB) phase of evolution, alternately burning hydrogen and helium in shells above an electron-degenerate carbon-oxygen (CO) core. The excess of carbon relative to oxygen at the surfaces of these stars is thought to be due to convective dredge-up which occurs following a thermal pulse. During a thermal pulse, carbon and neutron-rich isotopes are made in a convective helium-burning zone. In model stars of large CO core mass, the source of neutrons for producing the neutron-rich isotopes is the 22Ne(α, n)25Mg reaction and the isotopes are produced in the solar system s-process distribution. In models of small core mass, the 13C(α, n) 16O reaction is thought to be responsible for the release of neutrons, and the resultant distribution of neutron-rich isotopes is expected to vary considerably from one star to the next, with the distribution in isolated instances possibly resembling the solar system distribution of r-process isotopes. After the dredge-up phase following each pulse, the 13C is made by the reactions 12C(p,γ) 13N(β+ v) 13C in a zone of large 12C abundance and small 1H abundance that has been established by semiconvective mixing during the dredge-up phase. There is qualitative accord between the properties of carbon stars in the Magellanic Clouds and properties of model stars, but considerably more theoretical work is required before a quantitative match is achieved.

The observed paucity of AGB stars more luminous than MBOL ∼ −6 is interpreted to mean that the AGB lifetime of a star more luminous than this is at least a factor of ten smaller than the AGB lifetime of stars less luminous than this, or, at most 105 yr. Since, with current estimates of the 22Ne(α, n)25Mg reaction rate R22, only AGB model stars more luminous than MBOL ∼ −6 can produce s-process isotopes in the solar system distribution, it is inferred that either (1) the current estimates of R22 are too small by one to two orders of magnitude, allowing less luminous AGB stars to contribute, (2) the solar system distribution is not equivalent to the average Galactic distribution, being rather the consequence of a unique injection into the protosolar nebula of matter from a massive intermediate-mass AGB star, or (3) the estimates of the temperatures in the convective shell that are given by extant models are too low by, sav, 10 or 15 percent.

The absence of carbon stars more luminous than MBOL ∼ −6 is suggested to be due primarily to the fact that ∼ 106 yr of AGB evolution is necessary to produce surface C/O > 1, rather than to be due to the burning of dredged-up carbon into nitrogen at the base of the convective envelope during the interpulse quiescent hydrogen-burning phase. Thus, the positive correlation between the nitrogen and helium abundances in planetary nebulae is perhaps primarily a consequence of the second dredge-up episode rather than a consequence of processes occurring during the thermally pulsing phase.

Type
I. EVOLUTION OF LOW AND INTERMEDIATE MASS STARS OBSERVATIONS AND MODELS
Information
Symposium - International Astronomical Union , Volume 105: Observational Tests of the Stellar Evolution Theory , 1984 , pp. 3 - 19
Copyright
Copyright © Reidel 1984 

References

Becker, S.A. 1981, in Physical Processes in Red Giants , eds. Iben, I. Jr. and Renzini, A. (Dordrecht: Reidel), p. 141.CrossRefGoogle Scholar
Becker, S.A. 1983, in progress.Google Scholar
Becker, S.A. and Iben, I. Jr. 1979, Ap. J., 232, 831.Google Scholar
Becker, S.A. 1980, Ap. J., 237, 111.Google Scholar
Blanco, V.M., Frogel, J.A., and McCarthy, M.F. 1981, P.A.S.P., 93, 532.Google Scholar
Blanco, B.M., McCarthy, M.F., and Blanco, V.M. 1978, Nature, 271, 638.CrossRefGoogle Scholar
Blanco, V.M. and McCarthy, M.F. 1983, preprint.Google Scholar
Blanco, V.M., McCarthy, M.F., and Blanco, B.M. 1980, Ap. J., 242, 938.CrossRefGoogle Scholar
Cahn, J.H. 1980, Space Sci. Rev., 27, 457.Google Scholar
Cameron, A.G.W. 1955, Ap. J., 121, 144.CrossRefGoogle Scholar
Carbon, D.F., Langer, G.E., Butler, D., Kraft, R.P., Suntzeff, N.B., Kemper, E., Trezger, C.F., and Romanishin, W. 1983, Ap. J., 49, 207.Google Scholar
Chieffi, A. and Iben, I. Jr. 1983, in progress.Google Scholar
Cohen, J.G. 1982, Ap. J., 258, 143.Google Scholar
Cohen, J.G., Frogel, J.A., Persson, S.E., and Elias, J.H. 1981, Ap. J., 249, 481.CrossRefGoogle Scholar
Frogel, J. and Blanco, V.M. 1984, in Observational Tests of Stellar Evolution Theory , eds. Maeder, A. and Renzini, A. (Dordrecht: Reidel), p. 175.Google Scholar
Frogel, J. and Cohen, J.G. 1982, Ap. J., 253, 580.Google Scholar
Frogel, J. A., Cohen, J. G., Persson, S. E., and Elias, J. H. 1981, in Physical Processes in Red Giants , eds. Iben, I. Jr. and Renzini, A. (Dordrecht: Reidel), p. 159.Google Scholar
Frogel, J. and Whitford, A.E. 1982, Ap. J. Lett., 259, L7.Google Scholar
Fusi-Pecci, F. and Renzini, A. 1976, A. and Ap., 46, 447.Google Scholar
Iben, I. Jr. 1975a, Ap. J., 196, 525.Google Scholar
Iben, I. Jr. 1975b, Ap. J., 196, 549.Google Scholar
Iben, I. Jr. 1976, Ap. J., 208, 165.Google Scholar
Iben, I. Jr. 1977, Ap. J., 217, 788.Google Scholar
Iben, I. Jr. 1981, Ap. J., 246, 278.Google Scholar
Iben, I. Jr. 1982, Ap. J., 260, 821.Google Scholar
Iben, I. Jr. 1983a, Ap. J. Lett., 275, _____.Google Scholar
Iben, I. Jr. 1983b, in progress.Google Scholar
Iben, I. Jr. and Renzini, A. 1982, Ap. J. Lett., 263, L188.Google Scholar
Iben, I. Jr. and Renzini, A. 1983, Ann. Rev. Ast. and Ap., 21, 271.CrossRefGoogle Scholar
Iben, I. Jr. and Renzini, A. 1984, Physics Reports, in press.Google Scholar
Iben, I. Jr. and Truran, J.W. 1978, Ap. J., 230, 980.CrossRefGoogle Scholar
Kaler, J. B., Iben, I. Jr., and Becker, S. A. 1978, Ap. J. Lett., 224, L63.Google Scholar
Kraft, R. P. 1979, Ann. Rev. A. and Ap., 17, 309.Google Scholar
Kraft, R. P., Suntzeff, N. B., Langer, G. E., Carbon, D. F., Trefzger, Ch. F., Fried, E., and Stone, R. P. S. 1982, P.A.S.P., 94, 55.CrossRefGoogle Scholar
Iben, I. Jr. and Tutukov, A. V. 1984, Ap. J. Suppl., Feb. 1 issue.Google Scholar
Little-Marenin, I.R. and Little, S.J. 1979, A. J., 84, 1374.CrossRefGoogle Scholar
Lloyd-Evans, T. 1983, M.N.R.A.S., 205, _____.Google Scholar
McClure, R.D. 1983a, Ap. J., 268, 264.Google Scholar
McClure, R.D. 1983b, preprint.Google Scholar
McClure, R.D., Fletcher, J.M., and Nemec, J.M. 1980, Ap. J. Lett., 238, L35.Google Scholar
Nomoto, K. 1984, in Stellar Nucleosynthesis , eds. Chiossi, C. and Renzini, A. (Dordrecht: Reidel).Google Scholar
Olive, K. and Schramm, D.N. 1982, Ap. J., 257, 276.Google Scholar
Reimers, D. 1975, Mem. Soc. R. Sci. Liege, 6 Ser., 8, 369.Google Scholar
Renzini, A. and Voli, M. 1981, A. and Ap., 94, 175.Google Scholar
Richer, H.B. 1981, Ap. J., 243, 744.Google Scholar
Sanders, R. H. 1967, ApA J., 150, 971.Google Scholar
Schwarzschild, M. and Harm, R. 1967, Ap. J., 150, 961.Google Scholar
Searle, L., Wilkinson, A., and Bagnulo, W.G. 1980, Ap. J., 239, 803.Google Scholar
Sweigart, A. V. and Mengel, J. G. 1979, Ap. J., 229, 624.Google Scholar
Truran, J.W. and Iben, I. Jr. 1977, Ap. J., 216, 797.CrossRefGoogle Scholar
Whitford, A.E. and Rich, M. 1983, Ap. J., in press.Google Scholar
Wood, P.R. 1981, in Physical Processes in Red Giants , eds. Iben, I. Jr. and Renzini, A. (Dordrecht: Reidel), p. 135.Google Scholar
Wood, P.R., Bessel, M.S., and Fox, M.W. 1983, Ap. J., 272, 99.Google Scholar
Woosley, S. E., Axelrod, T. S., and Weaver, T. A. 1984, in Stellar Nucleosynthesis , eds. Chiosi, C. and Renzini, A. (Dordrecht: Reidel), p. 263.Google Scholar