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 = / 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.
Feast and Catchpole (1997 = FC97 hereafter) have recently published the first results on parallaxes to Galactic Cepheids based on measurements from the Hipparcos satellite. They list data for the 26 highest signal-to-noise Cepheid parallaxes; and after an extensive series of reductions (see their Table 2) they conclude that the best fit PL relation for the visual bandpass is MV = -2.81 log (P) - 1.43, with a standard error on the Hipparcos zero point of ± 0.10 mag, adopting the slope from prior work on LMC Cepheids. The authors go on to apply this V-band solution to determining the distance modulus of the LMC corrected for E (B-V) = 0.074 mag. Adding a metallicity correction of +0.042 mag and adopting < V >0 - log (P) from Caldwell & Laney (1991) gives (m-MV) 0LMC = 18.70 ± 0.10 mag. In this Letter we go beyond the V-band PL relation and explore the implications of the Hipparcos data for the multiwavelength calibrations of the Cepheid PL relation from the blue (B-band) out into the near infrared (2.2 µm K-band).