Measuring improved distances to nearby galaxies: The Araucaria Project
Wolfgang Gieren, Universidad de Concepcion
I will present an overview of our ongoing Araucaria Project which aims at the improvement of several of the most important stellar distance indicators, by determining their dependences on host galaxy environmental properties like metallicity and age, and at providing accurate distances to a set of nearby late-type galaxies which can be used to provide improved calibrations of secondary distance indicators, leading to a reduction of the current uncertainty on the Hubble constant. The talk will focus on recent progress we have made in using Cepheid variables, and blue supergiant stars as tools for distance measurement. I will show that by a combination of optical and near-infrared photometry of Cepheid variables, it seems now possible to derive the distances to nearby spiral and irregular galaxies with an accuracy of ~5%, considering systematic uncertainties like reddening, metallicity effects, and blending by unresolved companion stars. I will also present evidence that the slope of the period-luminosity relation is independent of metallicity in the range from -1.0 dex up to solar abundance. A preliminary calibration of the Flux-weighted Gravity-Luminosity Relationship for blue supergiants from VLT/FORS data will be presented, and its usefulness for distance measurement out to ~10 Mpc discussed.
