HipparcosParallaxes and the Cepheid Distance Scale

Hipparcos parallaxes have recently become available for a sample of Galactic Cepheids, and we have used these new distances to calibrate the Cepheid period-luminosity (PL) relation at six wavelengths ( BVIJHK ). Comparing these calibrations with previously published multiwavelength PL relations we find agreement to within 0.07 ± 0.14 mag, or 4% ± 7% in distance. Unfortunately, the current parallax errors for the fundamental pulsators (ranging in signal-to-noise ratio = π/σ π from 0.3 to 5.3, at best) preclude an unambiguous interpretation of the observed differences, which may arise from a combination of true distance modulus, reddening, and/or metallicity effects. We explore these effects and discuss their implications for the distance to the Large Magellanic Cloud (LMC) and the Cepheid-based extragalactic distance scale. These results suggest a range of LMC moduli between 18.44 ± 0.35 and 18.57 ± 0.11 mag; however, other effects on the Cepheid PL relation (e.g., extinction, metallicity, and statistical errors) are still as significant as any such reassessment of its zero point.