Elemental Abundances in the Cosmic Rays 26$\le $Z$\le $34 -- Evidence For Cosmic-Ray Origin in OB Associations

The TIGER instrument flew on high-altitude balloons over Antarctica for 50 days. The observed elemental abundances with 26$\le $Z$\le $34, when corrected for fragmentation during propagation in the Galaxy and in the atmosphere, show cosmic-ray source abundances that differ from the standard Solar System (SS) abundances. Preferential acceleration of refractory elements does not fully explain these differences. They can be accounted for by a source mixture of $\sim $80{\%} SS and $\sim $20{\%} representative of the ejecta from massive stars, which mixture is then affected by elemental volatility in the acceleration process. This 80/20 mixture has also been shown to account for the isotopic composition of lighter cosmic rays and can be understood as the result of cosmic-ray acceleration in OB associations.