The single-degenerate channel for the progenitor of type Ia supernovae   with different metallicities
  The single-degenerate channel for the progenitors of type Ia supernovae (SNe Ia) are currently accepted, in which a carbon-oxygen white dwarf (CO WD) accretes hydrogen-rich material from its companion, increases its mass to the Chandrasekhar mass limit, and then explodes as a SN Ia. Incorporating the prescription of \citet{HAC99a} for the accretion efficiency into Eggleton's stellar evolution code and assuming that the prescription is valid for \emph{all} metallicities, we performed binary stellar evolution calculations for more than 25,000 close WD binaries with metallicities $Z=0.06, 0.05, 0.04, 0.03, 0.02, 0.01, 0.004, 0.001, 0.0003$ and 0.0001. For our calculations, the companions are assumed to be unevolved or slightly evolved stars (WD + MS). As a result, the initial parameter spaces for SNe Ia at various $Z$ are presented in orbital period-secondary mass ($\log P_{\rm i}, M_{\rm 2}^{\rm i}$) planes. Our study shows that both the initial mass of the secondary and the initial orbital period increase with metallicity. Thus, the minimum mass of the CO WD for SNe Ia decreases with metallicity $Z$. The difference of the minimum mass may be as large as 0.24 $M_{\odot}$ for different Z.   Adopting the results above, we studied the birth rate of SNe Ia for various $Z$ via a binary population synthesis approach. If a single starburst is assumed, SNe Ia occur systemically earlier and the peak value of the birth rate is larger for a high $Z$. The Galactic birth rate from the WD + MS channel is lower than (but comparable to) that inferred from observations. Our study indicates that supernovae like SN2002ic would not occur in extremely low-metallicity environments, if the delayed dynamical-instability model in \citet{HAN06} is appropriate. 
X. Meng, X. Chen and Z. Han