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We undertake a new test of the metallicity sensitivity of the Leavitt Law forClassical Cepheids. We derive an empirical calibration of the apparentluminosities of Cepheids as measured from the optical through the mid-infrared(0.45-8.0um) as a function of spectroscopic [Fe/H] abundances of individualCepheids in the Large Magellanic Cloud from Romaniello et al. (2008). Thecumulative trend over the entire wavelength range shows a nearly monotonicbehavior. The sense of the trend is consistent with differentialline-blanketing in the optical, leading to stars of high metallicity beingfainter in the optical. This is followed by a reversal in the trend at longerwavelengths, with the cross-over occurring near the K band at about 2.2um,consistent with a subsequent redistribution of energy resulting in a mildbrightening of Cepheids (with increased metallicity) at mid-infraredwavelengths. This conclusion agrees with that of Romaniello et al. based on adifferential comparison of the mean V- and K-band Leavitt Laws for the Galaxy,SMC and LMC, but is opposite in sign to most other empirical tests of thesensitivity of Cepheid distances to mean [O/H] HII region abundances. We alsosearch for a correlation of Cepheid host-galaxy metallicity with deviations ofthe galaxy's Cepheid distance from that predicted from a pure Hubble flow.Based on Cepheid distances to 26 nearby galaxies in the local flow, only a veryweak signal is detected giving Dmu_o = -0.17 (+/- 0.31) ([O/H] - 8.80) - 0.21(+/-0.10). This is in agreement with previous determinations, but statisticallyinconclusive.

Two New Tests of the Metallicity Sensitivity of the Cepheid Period-Luminosity Relation (The Leavitt Law)