BEAT CEPHEID PERIOD RATIOS FROM OPAL OPACITIES

The discovery of a large number of beat Cepheids in the Large Magellan ic Cloud in the MACHO survey provides an opportunity to compare the ch aracteristics of such Cepheids over a range of metallicities. We produ ced a large grid of linear nonadiabatic pulsation models using the OPA L opacity tables and with compositions corresponding to those of the M ilky Way, and the Large and Small Magellanic Clouds. Using the relatio nship between the period ratio and the main pulsation period, we are a ble to define a range of models which correspond to the observed beat Cepheids, and thereby constrain the physical characteristics of the LM C beat Cepheids. We are also able to make some predictions about the n ature of the yet-to-be-discovered SMC beat Cepheids. (C) 1997 American Astronomical Society.