  We report the detections of low-mass companions to five M and L dwarfs within
10 pc of the Sun using the Hubble Space Telescope (HST) Near-Infrared Camera
and Multi-Object Spectrometer (NICMOS). Follow-up observations using the HST
Advanced Camera for Surveys (ACS) and Fine Guidance Sensor 1r (FGS1r) confirm
our NICMOS discoveries of companions to the L4.5 dwarf GJ 1001B (LHS 102B) and
the M5 dwarf LHS 224, respectively. Images obtained with the Astrophysical
Research Consortium 3.5 m telescope at Apache Point Observatory verify our
discovery of a companion to the M3 dwarf G 239-25. Our NICMOS images confirm
the previously suspected duplicity of the M3 dwarfs GJ 54 and GJ 84. The
components of GJ 1001BC and LHS 224AB have nearly equal luminosities in all the
ACS and/or NICMOS bandpasses in which they were observed. The magnitudes of GJ
54A and B in one FGS1r bandpass and four NICMOS bandpasses differ by <~ 1. GJ
84B and G 239-25B are ~4 magnitudes fainter than their M3 companions in the
NICMOS bandpasses. We estimate from our NICMOS photometry that GJ 84B and G
239-25B have spectral types M7 and M8, respectively, and masses near the lower
limit for sustained hydrogen burning. The apparent separations of GJ 1001BC, GJ
54AB, and LHS 224AB suggest orbital periods less than 5 yr. These binary dwarfs
are ideal candidates for continued astrometric monitoring that will quickly
yield accurate dynamic masses needed to constrain the mass-luminosity relation
for low-mass stars and brown dwarfs.
