Recent observations have revealed that Type Ia supernovae ( SNe Ia ) are not perfect standard candles but show some variations in their absolute magnitudes , light curve shapes , and spectra .
The C/O ratio in the SNe Ia progenitors ( C-O white dwarfs ) may be related to this variation .
In this work , we systematically investigate the effects of stellar mass ( M ) and metallicity ( Z ) on the C/O ratio and its distribution in the C-O white dwarfs by calculating stellar evolution from the main-sequence through the end of the second dredge-up for M = 3 - 9 M _ { \odot } and Z = 0.001 - 0.03 .
We find that the total carbon mass fraction just before SN Ia explosion varies in the range 0.36 – 0.5 .
We also calculate the metallicity dependence of the main-sequence-mass range of the SN Ia progenitor white dwarfs .
Our results show that the maximum main-sequence mass to form C-O white dwarfs decreases significantly toward lower metallicity , and the number of SN Ia progenitors may be underestimated if metallicity effect is neglected .
We discuss the implications of these results on the variation of SNe Ia , determination of cosmological parameters , luminosity function of white dwarfs , and the galactic chemical evolution .