Metal-poor turnoff and subgiant field stars in the Galaxy - I. RGU photometry in a high-latitude field near M101

Abstract

Photographic RGU photometry for about 1800 stars down to a limiting G-magnitude of 19.5 in a high-latitude field ((l, b) = (101 degrees, +60 degrees)) near the galaxy M101 is investigated. We use an improved variant of the classical three-color method which is based on recent UBV-RGU-photometric transforms and calibrations (Buser 1988; Buser & Fenkart 1990) and on models of the stellar density distributions of the Galactic population components.