Calibration of the Cepheid Distance Scale with the Infrared Surface Brightness Technique

Abstract

We review the process of determining the distances to Cepheid variables with the infrared surface brightness technique. We show that both versions of this technique (working with the V, V – K and the pure infrared K, J – K magnitude/color combinations) yield consistent distances to Cepheid variables. For a Cepheid with average-quality photometric and radial velocity data, the typical total uncertainty in the distance is ±5%. We use the distances of 34 Galactic variables to calibrate period-luminosity relations in the V, I, J, H, K bands and demonstrate that these relations lead to distance moduli of the LMC which agree to ±0.02 mag. The infrared surface brightness technique yields a best LMC distance modulus of 18.46 ±0.02. We discuss possible metallicity corrections, such as the ones determined by Sasselov et al. from EROS Cepheids comparison in the LMC and SMC, and conclude that our distance modulus is negligibly affected by these corrections. Finally, we present a program to obtain reddening- and metallicity-independent infrared surface brightness distances of Cepheid variables in LMC clusters which will yield an even more accurate mean LMC distance independent of any metallicity correction to Cepheid absolute magnitudes.