Often, the components of a binary system are not resolved, but the combined light is imaged as an oval. Direct imaging of a binary system, resolving the components into separate images, is the preferred method for determining the orbit parameters. For close faint companions, performing this task from the ground is difficult. The FOS images of Wolf 424 AB, a known candidate brown-dwarf pair, shows the companion is not following the predicted orbit. The revised orbit, including the FOS position of the companion, does not rule out the possibility that the component masses, or at least Wolf 424 B, are substellar and within the realm of brown dwarfs.
Astronomers are excited about discovering and studying brown dwarfs.
Brown dwarfs are objects that are smaller than a hydrogen burning star, but larger than the planet Jupiter. Brown dwarfs bridge the gap between the formation of stars and the formation of planets. The HST FOS imaging technique discussed above is being used to image the nearby stars in search of brown dwarfs. Four targets have been imaged to date, Wolf 359, Wolf 424 AB, GJ 1245 AC and Gl 293.