The MACHO Project LMC Variable Star Inventory. VIII. The Recent Star Formation History of the Large Magellanic Cloud from the Cepheid Period Distribution

We present an analysis of the period distribution of $\sim 1800$ Cepheids inthe Large Magellanic Cloud, based on data obtained by the MACHO microlensingexperiment and on a previous catalogue by Payne-Gaposchkin. Using stellarevolution and pulsation models, we construct theoretical period-frequencydistributions that are compared to the observations. These models reveal that asignificant burst of star formation has occurred recently in the LMC ($\sim1.15\times 10^8$ years). We also show that during the last $\sim 10^8$ years,the main center of star formation has been propagating from SE to NW along thebar. We find that the evolutionary masses of Cepheids are still smaller thanpulsation masses by $\sim 7$ % and that the red edge of the Cepheid instabilitystrip could be slightly bluer than indicated by theory. There are $\sim 600$Cepheids with periods below $\sim 2.5$ days cannot be explained by evolutiontheory. We suggest that they are anomalous Cepheids; a number of these starsare double-mode Cepheids.Comment: 29 pages, 4 figures, uses AAS LATeX 4.0. To appear in Astronomical Journal Feb 199