Stellar physical parameters from Str \"omgren photometry. Application to the young stars in the Galactic anticenter survey

TL;DR

This paper introduces a new model-based method using Str"omgren photometry to accurately determine distances and extinctions of young stars, improving upon classical calibrations and enabling detailed mapping of the Perseus arm.

Contribution

A novel, model-based approach for deriving stellar parameters from Str"omgren photometry, validated against Hipparcos data, and applied to a large sample of young stars in the Galactic anticenter.

Findings

Detected and quantified systematic trends in empirical photometric distances.

Proposed corrections for atmospheric grid shifts in specific temperature ranges.

Achieved more accurate stellar distances that align better with Hipparcos measurements.

Abstract

Aims. The aim is to derive accurate stellar distances and extinctions for young stars of our survey in the Galactic anticenter direction using the Str\"omgren photometric system. This will allow a detailed mapping of the stellar density and absorption toward the Perseus arm. Methods. We developed a new method for deriving physical parameters from Str\"omgren 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 Hbeta. Distances derived from both this method and the classical pre-Hipparcos calibrations were tested against Hipparcos parallaxes and found to be accurate. Results. Systematic trends in stellar photometric distances derived from empirical calibrations were detected and quantified. Furthermore, a shift in the atmospheric grids in the range Teff=[7000,9000]K was detected and a correction is proposed. The two methods were used to compute distances and reddening for about 12000 OBA-type stars in our Str\"omgren 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.