Radioactive Al26 and Fe60 in the Milky Way: implications of the RHESSI detection of Fe60

Abstract

The recent detection of gamma-ray lines from radioactive Al26 and Fe60 in the Milky Way by the RHESSI satellite calls for a reassessment of the production sites of those nuclides. The observed gamma-ray line flux ratio is in agreement with calculations of nucleosynthesis in massive stars, exploding as SNII (Woosley and Weaver 1995); in the light of those results, this observation would suggest then that SNII are the major sources of Al26 in the Milky Way, since no other conceivable source produces substantial amounts of Fe60. However, more recent theoretical studies find that SNII produce much higher Fe60/Al26 ratios than previously thought and, therefore, they cannot be the major Al26 sources in the Galaxy (otherwise Fe60 would be detected long ago, with a line flux similar to the one of Al26). Wolf-Rayet stars, ejecting Al26 (but not Fe60) in their stellar winds, appear then as a most natural candidate. We point out, however, that this scenario faces also an important difficulty. Forthcoming results of ESA's INTEGRAL satellite, as well as consistent calculations of nucleosynthesis in massive stars (including stars of initial masses as high as 100 M_sun and metallicities up to 3 Z_sun), are required to settle the issue.

arXiv comment6 pages, 4 figures, accepted in AA

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• Presupernova Evolution of Rotating Massive Stars I: Numerical Method and Evolution of the Internal Stellar Structure
• Nucleosynthesis in Massive Stars With Improved Nuclear and Stellar Physics
• Stellar evolution with rotation X: Wolf-Rayet star populations at solar metallicity
• Evolution, Explosion and Nucleosynthesis of Core Collapse Supernovae
• 26Al and 60Fe From Supernova Explosions
• The Reuven Ramaty High Energy Solar Spectroscopic Imager observation of the 1809 keV line from Galactic 26Al

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• Characterizing Supernova Progenitors via the Metallicities of their Host Galaxies, from Poor Dwarfs to Rich Spirals
• SPI observations of the diffuse 60Fe emission in the Galaxy
• New estimates of the contribution of Wolf--Rayet stellar winds to the Galactic 26Al
• Nuclear-Astrophysics Lessons from INTEGRAL
• 26Al in the Early Solar System: Not so Unusual After All
• Astrophysical constraints from gamma-ray spectroscopy
• Electron-capture supernovae as sources of 60Fe
• Detection of gamma-ray lines from interstellar 60Fe by the high resolution spectrometer SPI
• Gamma-ray Emission of 60Fe and 26Al Radioactivities in our Galaxy
• Deep-Ocean Crusts as Telescopes: Using Live Radioisotopes to Probe Supernova Nucleosynthesis
• ${}^{60}$Fe in core-collapse supernovae and prospects for X-ray and $\gamma$-ray detection in supernova remnants
• Nucleosynthetic Constraints on the Mass of the Heaviest Supernovae
• Distributions of Short-Lived Radioactive Nuclei Produced by Young Embedded Stellar Clusters
• Measuring 26Al and 60Fe in the Galaxy
• Progress in Nuclear Astrophysics of East and Southeast Asia
• Gamma-Ray Line Astronomy
• Measuring Cosmic Elements with Gamma-Ray Telescopes
• The Impact of the New ${}^{59}$Fe Decay Rates on ${}^{60}$Fe and ${}^{26}$Al Nucleosynthesis in Massive Stars