We present the completion of a program to cross-correlate the SDSS Data
Release 1 and 2MASS Point Source Catalog in search for extremely red L and T
dwarfs. The program was initiated by Metchev and collaborators, who presented
the findings on all newly identified T dwarfs in SDSS DR1, and estimated the
space density of isolated T0--T8 dwarfs in the solar neighbourhood. In the
current work we present most of the L dwarf discoveries. Our red-sensitive (z-J
> 2.75 mag) cross-match proves to be efficient in detecting peculiarly red L
dwarfs, adding two new ones, including one of the reddest known L dwarfs. Our
search also nets a new peculiarly blue L7 dwarf and, surprisingly, two M8
dwarfs. We further broaden our analysis to detect unresolved binary L or T
dwarfs through spectral template fitting to all L and T dwarfs presented here
and in the earlier work by Metchev and collaborators. We identify nine probable
binaries, six of which are new and eight harbour likely T dwarf secondaries. We
combine this result with current knowledge of the mass ratio distribution and
frequency of substellar companions to estimate an overall space density of
0.005--0.05 pc^{-3} for individual T0--T8 dwarfs.Comment: Accepted by Ap
