Increasing the census of L and T dwarfs in wide binary and multiple
  systems using Dark Energy Survey DR1 and Gaia DR2 data
  We present the discovery of 255 binary and six multiple system candidates
with wide > 5" separation composed by ultracool dwarfs companions to stars,
plus nine double ultracool dwarf systems. These systems were selected based on
common distance criteria. About 90% of the total sample has proper motions
available and 73% of the systems also satisfy a common proper motion criterion.
The sample of ultracool candidates was taken from the Dark Energy Survey (DES)
and the candidate stellar primaries are from Gaia DR2 and DES data. We compute
chance alignment probabilities in order to assess the physical nature of each
pair. We find that 174 candidate pairs with Gaia DR2 primaries and 81 pairs
with a DES star as a primary have chance alignment probabilities < 5%. Only
nine candidate systems composed of two ultracool dwarfs were identified. The
sample of candidate multiple systems is made up of five triple systems and one
quadruple system. The majority of the ultracool dwarfs found in binaries and
multiples are of early L type and the typical wide binary fraction over the L
spectral types is 2-4%. Our sample of candidate wide binaries with ultracool
dwarfs as secondaries constitutes a substantial increase over the known number
of such systems, which are very useful to constrain the formation and evolution
of ultracool dwarfs.
