New light on faint stars. II. A photometric study of the low luminosity main sequence.

The stellar main-sequence luminosity function is derived to absolute magnitude plus 19 from photometric observations of UK Schmidt telescope plates in the V, R, and I bands using the Cosmos automatic measuring machine. A complete sample has been made of every star in 18.24 square degrees towards the South Galactic Pole brighter than 17.0. Absolute magnitudes and distances are derived by photometric parallax. The photometrically defined luminosity function is in agreement with that derived from samples of nearby stars, using proper motion techniques, for absolute magnitudes from plus 9 to plus 19. No evidence for an excess of intrinsically faint stars is found, relative to the numbers found in kinematic surveys.