Radioactive Milky Way

Determining the Contribution of Massive Stars and Classical Novae to the Radioactive Isotope Al-26

The radioactive isotope Al-26 is produced in massive stars and injected in their wind phases and supernovae. Classical novae, that is, thermonuclear outbursts on the surface of accreting white dwarfs, are also believed to produce considerable amounts of Al-26. The differences for the two source types are the event rate (2 per century for supernovae vs. 1 peer week for novae) and the nucleosynthesis yields, i.e. how much Al-26 is produced on average. The gamma-ray observatory INTEGRAL measures the distribution of Al-26 through its decay (lifetiime 1 million years) gamma-ray line at photon energies around 1.809 MeV. The fractions which sources produce how much of the observed Al-26 are unknown. Determining these contributions would gauge stellar evolution models through the nucleosynthesis output of the population of massive stars and/or white dwarfs. In this work, the Al-26 mass as a function of distance to the Galactic Centre should be determined with an available 20 yr data set from INTEGRAL. A comparison with 1D Galactic Chemical Evolution models will then estimate the contributions of the stellar populations to the Al-26 content.

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