Faint optical spiral tracers

Extract

The use of modern photographic emulsions and techniques allows for the discovery of optical spiral tracers much fainter than was possible in the past. Our searches for such faint objects deal with the Puppis, Vela, Crux, Circinus, Norma and Ara regions of the Milky Way using Kodak plates (baked in dry nitrogen) obtained with the Curtis Schmidt-telescope at Cerro Tololo Inter-American Observatory. We have discovered OB stars as faint as 15 mag on IIIa-J plates obtained with the thin prism, and Hα emission-line objects (many of which are Be stars) as faint as 16 mag on 127-04 plates obtained with the 4° prism.