Cepheid Mass-Luminosity Relations from the Magellanic Clouds

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  • 20 October 2000
Abstract
The OGLE data base is used to obtain periods, effective temperatures and luminosities for fundamental and overtone Magellanic Cloud Cepheids. Masses are then computed for these stars with our linear code with turbulent convection assuming an average composition of (X=0.716, Z=0.010) for the LMC and of (X=0.726, Z=0.004) for the SMC. The average M-L relation for the fundamental Cepheids matches closely that for the first overtone Cepheids, this for each Magellanic Cloud. Neither the SMC nor the LMC average Log M-Log L relations are straight lines, but have a noticeable curvature. Our analysis clearly excludes the short distances for both clouds that were adopted by OGLE on the basis of the red clumps. The current evolutionary tracks systematically predict smaller luminosities than observed, especially at high luminosity. Moreover, the evolutionary tracks of the low mass stars are not in agreement with the observations as they do not extend sufficiently blueward and do not penetrate deep enough into the instability strip, or not at all.

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