TESTING MASS LOSS IN LARGE MAGELLANIC CLOUD CEPHEIDS USING INFRARED AND OPTICAL OBSERVATIONS

It has been claimed that period-luminosity (P-L) relations derived from infrared observations of Large Magellanic Cloud (LMC) Cepheids are less dependent on the metallicity of the Cepheids. In this work, infrared observations of LMC Cepheids from the SAGE survey are combined with OGLE II optical observations to model and predict mass-loss rates. The mass-loss rates are fit to the data and are predicted to range from about 10(-12) to 10(-7) M-circle dot/yr; however, the rates depend on the assumed value of the dust-to-gas ratio. By comparing the relations derived from observations to the relations derived from predicted infrared stellar luminosities from the mass-loss model, it is shown that mass loss affects the structure and scatter of the infrared P-L relation. Mass loss produces shallower slopes of the infrared relations and a lower zero point. There is also evidence for nonlinearity in the predicted P-L relations, and it is argued that mass loss produces larger infrared excess at lower periods, which affects the slope and zero point, making the P-L relations more linear in the wavelength range of 3.6 to 5.8 mu m. Because the dust-to-gas ratio is metallicity dependent and mass loss may have a metallicity dependence, infrared P-L relations have additional uncertainty due to metallicity.