We propose a new method to measure the metallicity of Type Ia supernova progenitors using Mn and Cr lines in the X-ray spectra of young supernova remnants .
We show that the Mn to Cr mass ratio in Type Ia supernova ejecta is tightly correlated with the initial metallicity of the progenitor , as determined by the neutron excess of the white dwarf material before thermonuclear runaway .
We use this correlation , together with the flux of the Cr and Mn K \alpha X-ray lines in the Tycho supernova remnant recently detected by Suzaku ( Tamagawa et al . 2008 ) to derive a metallicity of log ( Z ) = -1.32 ^ { +0.67 } _ { -0.33 } for the progenitor of this supernova , which corresponds to log ( Z / Z _ { \odot } ) = 0.60 ^ { +0.31 } _ { -0.60 } according to the latest determination of the solar metallicity by Asplund et al .
( 2005 ) .
The uncertainty in the measurement is large , but metallicities much smaller than the solar value can be confidently discarded .
We discuss the implications of this result for future research on Type Ia supernova progenitors .