Supernova electron capture rates on odd-odd nuclei

At densities between 108 and 1010 g/cm3 electron capture in a presupernova collapse is believed to mainly occur on odd-odd nuclei. We have derived the rates for six of the most important electron capturing nuclei, 54,56,58Mn and 56,58,60Co, based on calculations of the Gamow-Teller strength distributions for the ground states and first excited states. These calculations have been performed by shell model diagonalization in the pf shell using a recently modified version of the KB3 interaction. The shell model rates are noticeably smaller than the presently adopted rates as the latter have been derived by placing the Gamow-Teller (GT) resonance at too low excitation energies.