Distribution of stars in the disk

Abstract

Recent developments in determining the large‐scale structure of the Galaxy with stellar tracers are discussed. Among the possible approaches, direct mapping using standard candles is emphasized because of its promise to provide the most unbiased and consistent view, especially when kinematic data is available.Candidate standard candle tracers include HII regions, planetary nebulae, Cepheid variables, and AGB stars (carbon stars, Mira variables, OH/IR stars). Current progress is briefly reviewed in turn. Mapping techniques are discussed, and as an example, the author’s experience analyzing the IRAS PSC and detection of a bar is described.Bars and similar rotating non‐axisymmetric features in the Galaxy provide observable stellar kinematic signatures, even if the perturbations are relatively weak (several percent). Therefore, only a modest velocity data set is required to place meaningful constraints. For example, the moderate‐strength bar with half‐length of 3 kpc described previously will produce a strong...