CfA Colloquium Schedule Fall 2010
 14 October 2010

14 October 2010

Speaker: Martin Israel (Washington University, St. Louis)

Title:The Origin of Galactic Cosmic Rays

Abstract:Measurements of the elemental and isotopic composition of galactic cosmic rays point to their origin in OB associations at the core of galactic superbubbles. The Trans Iron Galactic Element Recorder (TIGER) has measured the elemental composition of the rare elements heavier than 26Fe, up to 38Sr, at energies from several hundred MeV/nucleon to tens of GeV/nucleon. These TIGER measurements were carried out during 50 days of stratospheric balloon flights over Antarctica. The Cosmic Ray Isotope Spectrometer (CRIS) has measured the isotopic composition of cosmic-ray elements from 4Be through 28Ni with energies between 50 and 500 MeV/nucleon as well as the elemental composition of heavier elements. The CRIS instrument is on the ACE spacecraft near the L1 Lagrange point, where it has been sending data since late 1997. While the abundances of elements and isotopes at the cosmic-ray source are broadly similar to the abundances in the Sun and meteorites, there are differences that point to a source enriched in the outflows of massive stars, which are mainly found in OB associations.

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