THE SOFTEST X-RAY SOURCES IN THE ROSAT POINTED CATALOG - WGACAT

We present a selection of X-ray sources with the softest observed spec tral characteristics and discuss their nature. These ''ultrasoft'' sou rces were detected in 3 years of pointings with the ROSAT. These sourc es are predominantly found to be white dwarfs, magnetic cataclysmic va riables, nearby late-type stars, and very X-ray soft active galactic n uclei. The broadband colors of the unidentified ultrasoft sources sugg est that a number of them may have at least two components in their sp ectrum, as for example, is found in most cataclysmic variables. Some o f these objects may represent the extreme of their respective populati ons, for example, unusual galaxies, ''supersoft'' sources with steep l ow-energy spectrum and high X-ray luminosity (similar to 10(38) ergs s (-1)), active galactic nuclei, stars, etc. Follow-up studies in the op tical and other wavebands are needed.