High-resolution near-infrared J-band imaging with the Subaru Telescope has
demonstrated, for the first time from the ground, two independent jets eman
ating from the protostar L 1551 IRS 5. Successive near-infrared spectroscop
y has revealed that the jet emission is dominated by [Fe II] lines in the J
- and H-bands. While the visual-extinction estimated from the [Fe II] line
ratios reaches more than 20 mag in the close vicinity of IRS 5, it decrease
s rapidly at similar to 1 " from 1RS 5 and remains constant around 7 mag at
larger distances. The electron density in the jets is estimated to be 10(6
) cm(-3) near IRS 5 and is 10(4) to 10(5) cm(-3) in their outer section. Th
e twisted appearance of the jets, with bright knots especially prominent in
the northern jet, is similar to the R-band jets observed with the Hubble S
pace Telescope. These results suggest that the twisted structure and bright
emission knots are intrinsic to the jets and are not due to a spatial vari
ation of the extinction.