We propose to search for nearby brown dwarfs as companions to
 nearby white dwarfs within 20 pc from the Sun selected from
 the Gliese/Jahreiss Catalog, a complete sample of 50 targets.
 These white dwarfs are old objects (several Gyr) so that
 any companion brown dwarfs are expected to have cooled to
 200-1000 Kelvin, ideal for detection of an infrared excess
 in the 3-15 micron range. In fact, white dwarfs are
 the perfect targets to search for brown dwarf companions, as
 their radius is 10 times smaller than brown dwarf radii
 so that the brown dwarf blackbody emission curve can cross
 and exceed the white dwarf blackbody emission in the infrared.
 Our search is different from the Zuckerman and Becklin surveys
 which concentrated on young (< 1 Gyr) white dwarfs so that any
 young brown dwarf companions could be detected from the ground
 at 1-2 microns. By choosing a sample of OLD white dwarfs we make
 sure that any infrared companion must be a bona fide brown dwarf
 (ie an object with a temperature much lower than that of an M8-M10
 Main Sequence star, hence a mass below the hydrogen burning limit).
 We need ISO because ground-based observations do not have the
 necessary sensitivity by a factor of 100 (1 mJy at 10 mu is needed).
 We will use ISOCAM (1.5"/pixel) with the SW1, LW2, and LW3 filters.
 ISOCAM is also 2 orders of magnitude more sensitive than IRAS
 at 12 mu, enough to detect cool (e.g. 750 K) brown dwarfs at 20 pc.
 The choice of 3 filters ensures that we can cover the range of
 effective temperatures expected for brown dwarfs with ages 3-10 Gyr.
 ISOCAM is preferred over ISOPHOT since imaging with ISOCAM allows us
 1) to register any infrared excess emission coincident with a white
 dwarf, 2) to discover cool companions near the white dwarfs, and 3)
 to check that there is no confusion with cool background objects
 (e.g. obscured high-z protogalaxies which we may happen to detect).