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 about 1800 Cepheids in the LMC, based on data obtained by the MACHO microlensing experiment and o n a previous catalog by C. H. Payne Gaposchkin. Using stellar evolution and pulsation models, we construct theoretical period-frequency distributions that are compared with the observations. These models reveal that a signifi cant burst of star formation has occurred recently in the LMC (similar to 1 .15 x 10(8) yr). We also show that during the last similar to 10(8) yr, the main center of star formation has been propagating from southeast to north west along the bar. We find that the evolutionary masses of Cepheids are st ill smaller than pulsation masses by similar to 7% and that the red edge of the Cepheid instability strip could be slightly bluer than indicated by th eory. There are approximately 600 Cepheids with periods below similar to 2. 5 days that cannot be explained by evolution theory. We suggest that they a re anomalous Cepheids and that a number of these stars are double-mode Ceph eids.