The formation of ²⁶Al in nova explosions

The amount of ²⁶Al in the interstellar medium, which has been detected both by the HEAO 3 γ-ray spectrometer and the SMM experiment, in combination with the measured overabundance of ²⁶Mg in meteorites, is predicted to have been produced by nucleosynthesis in nova explosions. To test this prediction, we have investigated the nucleosynthesis of ²⁶Al during hot hydrogen burning along temperature-density-time profiles obtained from hydrodynamic simulations of nova outbursts. We find that we can predict the yield of ²⁶Al if we characterize the thermonuclear runaway by means of two parameters: (1) the peak temperature and (2) the time required by the nova to reach peak temperature. We provide yields of ²⁶Al in terms of these parameters. We have also found that the yield of ²⁶Al is directly proportional to the abundances of the heavy elements so that about 20% of the initial ²⁴Mg is converted into ²⁶Al. Therefore, we are also able to show that the dominant contributor of ²⁶Al to the Galaxy must be novae which occur on oxygen-neon-magnesium white dwarfs. However, we also find that the class of novae that should be the most important contributors to Galactic nucleosynthesis of ²⁶Al may not have been discovered but must exist.