The zero point of the Cepheid period-luminosity relation in the 1.05 micron wave band
New observations of the Cepheids in the galactic clusters and externalgalaxies LMC, NGC 6822, NGC 300, and Sex A in the 1.05-micron wave band(IV) are presented. The slope of the P-L(IV) relation derived from theCepheids in the LMC agree with that in the SMC and that obtained forGalactic Cepheids. The zero point of the relation has been determinedfrom the distances to the galactic Cepheid clusters obtained throughZAMS fitting and referenced to the Pleiades modulus of 5.57. Thebolometric P-L relations derived individually using the data in V, J, Kwave bands are found to have the same slope and the zero point asobserved in the IV wave band. The comparison of the bolometric P-Lrelation with that obtained theoretically by Becker, Iben, and Tuggleshows agreement in the value of the slope. But the theoreticalmagnitudes are brighter by 0.4 mag. The true distance moduli to the LMC,the SMC, NGC 6822, NGC 300, and Sex A have been derived from P-L(IV)data and are found to be as 18.42, 18.83, 23.18, 25.72, and 25.27,respectively.
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