  The universality of the Cepheid Period-Luminosity relations has been under
discussion since metallicity effects have been assumed to play a role in the
value of the intercept and, more recently, of the slope of these relations. The
goal of the present study is to calibrate the Galactic PL relations in various
photometric bands (from B to K) and to compare the results to the
well-established PL relations in the LMC. We use a set of 59 calibrating stars,
the distances of which are measured using five different distance indicators:
Hubble Space Telescope and revised Hipparcos parallaxes, infrared surface
brightness and interferometric Baade-Wesselink parallaxes, and classical
Zero-Age-Main-Sequence-fitting parallaxes for Cepheids belonging to open
clusters or OB stars associations. A detailed discussion of absorption
corrections and projection factor to be used is given. We find no significant
difference in the slopes of the PL relations between LMC and our Galaxy. We
conclude that the Cepheid PL relations have universal slopes in all photometric
bands, not depending on the galaxy under study (at least for LMC and Milky
Way). The possible zero-point variation with metal content is not discussed in
the present work, but an upper limit of 18.50 for the LMC distance modulus can
be deduced from our data.
