SIMBAD references

The production of ²⁶Al in asymptotic giant branch (AGB) stars is studied based on evolutionary stellar models of different masses (1.5≤M/M_☉≤6) and metallicities (0.004≤Z≤0.02). It is confirmed that ²⁶Al is efficiently produced by hydrogen burning, but destruction of that nuclei by n-capture reactions during the interpulse and pulse phases becomes increasingly more efficient as the star evolves on the AGB. The amount of ²⁶Al available in the intershell region follows, at a given metallicity, a very well defined pattern as a function of the H-burning shell temperature T_H. Two zones must be distinguished. The first one comprises those He-rich layers containing H-burning ashes which escape pulse injection. The amount of ²⁶Al in that zone (1-2x10^–7M_☉ at the first pulse in 1.5-3M_☉ Z=0.02 stars) steadily decreases with pulse number. Its contribution to the surface ²⁶Al enhancement can only be important during the first pulses if dredge-up occurs at that stage. The second zone consists of the C-rich material emerging from the pulses. The amount of ²⁶Al available in that zone is higher than that in the first zone (3-4x10^–7M_☉ at the first pulse in 1.5-3M_☉ Z=0.02 stars), and keeps constant during about the first dozen pulses before decreasing when T_H>55x10⁶K. This zone is thus an important potential reservoir for surface ²⁶Al enrichment. Using third dredge-up (3DUP) efficiencies from model calculations, the surface ²⁶Al abundance is predicted to reach 1-2x10^–7 mass fractions in our low-mass solar metallicity stars, with an uncertainty factor of about three. It decreases with increasing stellar mass, being about three times lower in a 4M_☉ than in 2-3M_☉ stars. In massive AGB stars, however, hot bottom burning enables to easily reach surface ²⁶Al mass fractions above 10^–6. The ²⁶Al/²⁷Al ratios measured in meteoritic SiC and oxide grains are discussed, as well as that possibly measured in the nearby C-star IRC+10216. We also address the contribution of AGB stars to the 2-3M_☉ present day mass of ²⁶Al detected in the Galaxy. Finally, we discuss the possibility of directly detecting an AGB star or a planetary nebula as a single source at 1.8MeV with the future INTEGRAL satellite.