Secondary Fe-peak nuclei in the Tycho Supernova Remnant: A Promising   Tracer of Type Ia Progenitor Metallicity
  The Mn to Cr mass ratio in supernova ejecta has recently been proposed as a tracer of Type Ia SN progenitor metallicity. We review the advantages and problems of this observable quantity, and discuss them in the framework of two Galactic supernova remnants: the well known Tycho SNR and W49B, an older object that has been tentatively classified as Type Ia. The fluxes of the Mn and Cr Ka lines in the X-ray spectra of these SNRs observed by the Suzaku and ASCA satellites suggest progenitors of supersolar metallicity for both objects. 
Carles Badenes, Eduardo Bravo and John P. Hughes