The Optical Gravitational Lensing Experiment. Cepheids in the Magellanic Clouds. III. Period-Luminosity-Color and Period-Luminosity Relations of Classical Cepheids

摘要

We present Period-Luminosity-Color and Period-Luminosity relations ofclassical Cepheids constructed for about 1280 Cepheids from the LMC and 2140from the SMC. High quality BVI observations (120-360 epochs in the I-band and15-40 in the BV-bands) were collected during the OGLE-II microlensingexperiment. The I-band diagrams of the LMC show very small scatter,\sigma=0.074 mag, indicating that Cepheid variables can potentially be a verygood standard candle. We compare relations of fundamental mode Cepheids fromthe LMC and SMC and we do not find significant differences of slopes of thePeriod-Luminosity- Color and Period-Luminosity relations in these galaxies. Forthe first overtone Cepheids a small change of the slope of Period-Luminosityrelation is possible. We determine the difference of distance moduli betweenthe SMC and LMC with Cepheid relations and compare the result with differenceobtained with other standard candles: RR Lyr and red clump stars. Results arevery consistent and indicate that the values of zero points of the fundamentalmode Cepheid relations are similar in these galaxies. The mean difference ofdistance moduli between the SMC and LMC is equal to \mu_SMC-\mu_LMC=0.51\pm0.03mag. We calibrate the Period-Luminosity-Color and Period-Luminosity relationsfor classical, fundamental mode Cepheids using the observed LMC relations andadopting the short LMC distance modulus, \mu_LMC=18.22\pm0.05 mag, resultingfrom the recent determination with eclipsing system HV2274, RR Lyr and redclump stars and consistent with observations of Cepheids in NGC4258 galaxy, towhich precise geometric distance is known. Finally, we determine a constrainton the absolute magnitude of Cepheids by comparison of their mean V-bandmagnitude with that of RR Lyr stars in both Magellanic Clouds.