Asymptotic giant branch stars

Theoretical models for nucleosynthesis in asymptotic giant branch stars predict a large contribution to the cosmic nitrogen abundance from intermediate-mass stars [1], In particular, hot-bottom-burning in stars above a certain mass produces [C/N] —1 [2]. However, observations of C and N abundances in C-rich, metal-poor stars, usually using the CH and CN bands, show [C/N] values that vary between —0.5 and 1.5. (Fig. 1). If any of these stars have been polluted by intermediate mass AGB stars, then they should have lower [C/N] ratios. However, most of the CH stars with detailed abundances have [C/Fe] > 1.0, and it is more likely than stars mildly enhanced in C have been polluted by N-rich stars. 

Busfield A, Gilmour JD, Whitby JA, Turner G (2004) Iodine-xenon analysis of ordinary chondrite halide implications for early solar system water. Geochim Cosmochim Acta 68 195-202 Busso M, Gallino R, Wasserburg GJ (1999) Nucleosynthesis in asymptotic giant branch stars relevance for galactic enrichment and solar system formation. Annu Rev Astronom Astrophys 37 239-309 Cameron AGW (1969) Physical conditions in the primitive solar nebula. In Meteorite Research. Millman PM (ed) Reidel, Dordrecht, p 7-12... 

Herwig, F. (2005) Evolution of asymptotic giant branch stars. Annual Reviews of Astronomy and Astrophysics, 43, 435-479. An excellent discussion of the evolution of AGB stars. 

Smith, V. V. and Lambert, D. L. (1990) The chemical composition of red giants. III. Further CNO isotopic and -process abundances in thermally pulsing asymptotic giant branch stars. Astrophysical Journal Supplement, 72, 387—416. 

Figure 2.3 Dust production and gas mass return rate by different stellar types in solar masses per year and kpc-2 in the galaxy at the solar cycle. Stars produce mainly silicate or carbon dust only in some cases is a different kind of dust material formed, probably iron or some iron alloy (peculiar dust). Many additional dust components with much smaller abundance are formed in most cases (Data from Tielens 1999 Zhukovska el al. 2008). Abbreviations of stellar types AGB = asymptotic giant branch stars of spectral types M, S, or C OB = massive stars of spectral types O and B on or close to the main sequence RGB = massive stars on the red giant branch LBV = luminous blue variables WCL = Wolf-Rayet stars from the lower temperature range Novae = mass ejecta from novae SN = mass ejecta from supemovae.

AGB star asymptotic giant branch star, a cool and luminous red giant star. These evolved stars drive an intense wind that removes material from the surface at an increasing rate as the end of its lifecyle approaches. AGB stars are the proposed source of many types of presolar grains. 

Busso M., Gallino R., and Wasserburg G. J. (1999) Nucleosynthesis in asymptotic giant branch stars relevance for galactic enrichment and solar system formation. Ante Rev. Astron. Astrophys. 37, 239—309. 

Boothroyd A. I., Sackmann I.-J., and Wasserburg G. J. (1995) Hot bottom burning in asymptotic giant branch stars and its etfect on oxygen isotopic abundances. Astrophys. J. 442, L21-L24. 

Brown L. E. and Clayton D. D. (1992) SiC particles from asymptotic giant branch stars Mg burning and the s-process. Astrophys. J. 392, L79-L82. 

Hoppe P., Annen P., Strebel R., Eberhardt P., GaUino R., Lugaro M., Amari S., and Lewis R. S. (1997) Meteoritic silicon carbide grains with unusual Si-isotopic compositions evidence for an origin in low-mass metallicity asymptotic giant branch stars. Astropkys. J. 487, LlOl—L104. 

Lugaro M., Davis A. M., Gallino R., Pellin M. J., Straniero O., and Kappeler F. (2003) Isotopic compositions of strontium, zirconium, molybdenum, and barium in single presolar SiC grains and asymptotic giant branch stars. Astrophys. J. 593, 486-508. 

Arlandini, C., Kappeler, F., Wisshak, K., Gallino, R., Lugaro, M., Busso, M. Straniero, O. 1999 Neutron capture in low-mass asymptotic giant branch stars Cross sections and abundance signatures. ApJ 525, 886. 

Plez, B., Smith, V.V. Lambert, D.L. 1993 Lithium abundances and other clues to envelope burning in Small Magellanic Cloud asymptotic giant branch stars. ApJ 418, 812. 

The weighted mean value of variation in a they obtained was considerably smaller than that claimed by Murphy et al. (2003). Chand et al. found Aa/a = (—0.06 0.06) X 10 5. Furthermore, in a separate study, Ashenfelter et al. (2004) have shown that the synthesis of Mg in low-metallicity asymptotic giant-branch stars produces isotopic ratios that could explain the data from z < 1.8 without invoking variations in the fine structure constant. However, even for extremely low metallicity (inconsistent with that observed in the 0.4 z 2 redshift range), the expected effect produced by the different isotopic ratios is smaller than the one claimed by Murphy et al. (2003). Clearly, much more work on this topic is needed. I should also note right away that, in order not to be in conflict with the yield of " He, IAq /q I cannot exceed c. 2 x 10 at the time of nucleosynthesis (see, for example, Bergstrom et al., 1999). 

Stars less massive than about 8 M0 will avoid the supernova fate. In the 3-8 Mq range, helium ignition occurs in a non-degenerate core, so is not explosive. Core helium burning is associated with a blueward loop through the Cepheid instability strip, after which the star develops a double shell structure and becomes an asymptotic giant branch star. 

H. J. Habing, H. Olofsson in Asymptotic Giant Branch Stars, Springer (2004)... 

A. I. Karakas in Asymptotic Giant Branch Stars their influence on binary systems and the interstellar medium, PhD thesis, Monash University (2003)... 

Busso, M. Gallino, R. Wasserburg, G. J. Nucleosynthesis in Asymptotic Giant Branch Stars Relevance for Galactic Enrichment and Solar System Formation. Am. Rev. Astr. Astrophys. 1999, 37,239-309. 

Habing, H.J. Olofsson, H. (eds.) Asymptotic giant branch stars. Springer, Berlin, 2003, pp. 559. 

Asymptotic Giant Branch Stars (AGB) A period of stellar evolution. They are named for their place in a region on the Hertzsprung-Russell Diagram dominated by evolving low to medium-mass stars (0.6-10 solar masses). 

F. (2003) Isotopic composition of strontium, zirconium, molybdenum and barium in single presolar SiC grains and asymptotic giant branch stars. Astrophys. 

---