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The extragalactic distance scale builds directly on the CepheidPeriod-Luminosity (PL) relation as delineated by the sample of Cepheids in theLarge Magellanic Cloud (LMC). However, the LMC is a dwarf irregular galaxy,quite different from the massive spiral galaxies used for calibrating theextragalactic distance scale. Recent investigations suggest that not only thezero-point but also the slope of the Milky Way PL relation differ significantlyfrom that of the LMC, casting doubts on the universality of the Cepheid PLrelation. We want to make a differential comparison of the PL relations in thetwo galaxies by delineating the PL relations using the same method, theinfrared surface brightness method (IRSB), and the same precepts. The IRSBmethod is a Baade-Wesselink type method to determine individual distances toCepheids. We apply a newly revised calibration of the method as described in anaccompanying paper (Paper I) to 36 LMC and five SMC Cepheids and delineate newPL relations in the V,I,J, & K bands as well as in the Wesenheit indices in theoptical and near-IR. We present 509 new and accurate radial velocitymeasurements for a sample of 22 LMC Cepheids, enlarging our earlier sample of14 stars to include 36 LMC Cepheids. The new calibration of the IRSB method isdirectly tied to the recent HST parallax measurements to ten Milky WayCepheids, and we find a LMC barycenter distance modulus of 18.45+-0.04 (randomerror only) from the 36 individual LMC Cepheid distances. We find a significantmetallicity effect on the Wvi index gamma(Wvi)=-0.23+-0.10 mag/dex as well asan effect on the slope. The K-band PL relation on the other hand is found to bean excellent extragalactic standard candle being metallicity insensitive inboth slope and zero-point and at the same time being reddening insensitive andshowing the least internal dispersion.

astronomy and astrophysics

Calibrating the Cepheid Period-Luminosity relation from the infrared  surface brightness technique II. The effect of metallicity, and the distance  to the LMC