AAS 207th Meeting, 8-12 January 2006
Session 132 Views of the Magellanic Clouds Across Wavelengths
Poster, Wednesday, 9:20am-6:30pm, January 11, 2006, Exhibit Hall

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[132.05] Why the LMC Cepheid PL relation is non-linear at a period of 10 days.

S. M. Kanbur, C. C. Ngeow (University of illinois)

We present the case for a Cepheid period-luminosity relation in the LMC which is ``broken" at a period of 10 days using OGLE, MACHO, 2MASS data as well as other long period photometry. We show that rigorous statistical procedures reveal that these data are more consistent with two lines of significantly differing slope, but continuous at a period of 10 days. Viewed as a function of phase, the period-luminosity and period-color relations provide clear and compelling evidence of this break. We estimate the effect on the cosmic distance scale and use non-linear pulsation models to suggest a possible theoretical explanation which also explains the period-color properties of RR Lyrae stars.

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