Hipparcos Parallaxes 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 periodluminosity (PL) relation at six wavelengths (BV IJHK). 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 = π/σπ 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, statistical errors) are still as significant as any such reassessment of its zero point. Subject headings: Cepheids – Magellanic Clouds – infrared: stars