2014A&A...568A.119M

The aim is to derive accurate stellar distances and extinctions for young stars of our survey in the Galactic anticenter direction using the Stroemgren photometric system. This will allow a detailed mapping of the stellar density and absorption toward the Perseus arm. We developed a new method for deriving physical parameters from Stroemgren photometry and also implemented and tested it. This is a model-based method that uses the most recent available stellar atmospheric models and evolutionary tracks to interpolate in a 3D grid of the unreddened indexes [m₁], [c₁] and Hβ. Distances derived from both this method and the classical pre-Hipparcos calibrations were tested against Hipparcos parallaxes and found to be accurate. Systematic trends in stellar photometric distances derived from empirical calibrations were detected and quantified. Furthermore, a shift in the atmospheric grids in the range T_eff=[7000,9000]K was detected and a correction is proposed. The two methods were used to compute distances and reddening for ∼12000 OBA-type stars in our Stroemgren anticenter survey. Data from the IPHAS and 2MASS catalogs were used to complement the detection of emission line stars and to break the degeneracy between early and late photometric regions. We note that photometric distances can differ by more than 20%, those derived from the empirical calibrations being smaller than those derived with the new method, which agree better with the Hipparcos data.