Chemical evolution of the Large Magellanic Cloud
  We adopt a new chemical evolution model for the Large Magellanic Cloud (LMC)
and thereby investigate its past star formation and chemical enrichment
histories. The delay time distribution of type Ia supernovae recently revealed
by type Ia supernova surveys is incorporated self-consistently into the new
model. The principle results are summarized as follows. The present gas mass
fraction and stellar metallicity as well as the higher [Ba/Fe] in metal-poor
stars at [Fe/H]<-1.5 can be more self-consistently explained by models with
steeper initial mass functions. The observed higher [Mg/Fe] (> 0.3) at [Fe/H] ~
-0.6 and higher [Ba/Fe] (>0.5) at [Fe/H] ~ -0.3 can be due to significantly
enhanced star formation about 2 Gyr ago. The observed overall [Ca/Fe]-[Fe/H]
relation and remarkably low [Ca/Fe] (<-0.2) at [Fe/H]>-0.6 are consistent with
models with short-delay supernova Ia and with the more efficient loss of Ca
possibly caused by an explosion mechanism of type II supernovae. Although the
metallicity distribution functions do not show double peaks in the models with
a starburst about 2 Gyr ago, they show characteristic double peaks in the
models with double starbursts at ~200 Myr and ~2 Gyr ago. The observed apparent
dip of [Fe/H] around ~1.5 Gyr ago in the age--metallicity relation can be
reproduced by models in which a large amount (~10^9 M_{sun}) of metal-poor
([Fe/H]<-1) gas can be accreted onto the LMC.
