Radioactive Al and Fe in the Milky Way: Implications of the RHESSI detection of Fe

Institut d'Astrophysique de Paris, 98bis Bd. Arago, 75104 Paris, France

Corresponding author: prantzos@iap.fr

Received: 28 November 2003
Accepted: 14 March 2004

Abstract

The recent detection of gamma-ray lines from radioactive ²⁶Al and ⁶⁰Fe 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 & Weaver [CITE]); in the light of those results, this observation would suggest then that SNII are the major sources of ²⁶Al in the Milky Way, since no other conceivable source produces substantial amounts of ⁶⁰Fe. However, more recent theoretical studies find that SNII produce much higher ⁶⁰Fe/²⁶Al ratios than previously thought and, therefore, they cannot be the major ²⁶Al sources in the Galaxy (otherwise ⁶⁰Fe would be detected long ago, with a line flux similar to the one of ²⁶Al). Wolf-Rayet stars, ejecting ²⁶Al (but not ⁶⁰Fe) 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  and metallicities up to 3 ), are required to settle the issue.