We present SMA CO ( 2–1 ) observations toward the protostellar jet driven by SVS 13 A , a variable protostar in the NGC 1333 star-forming region .
The SMA CO ( 2–1 ) images show an extremely high-velocity jet composed of a series of molecular “ bullets ” .
Based on the SMA CO observations , we discover clear and large systematic velocity gradients , perpendicular to the jet axis , in the blueshifted and redshifted bullets .
After discussing several alternative interpretations , such as twin-jets , jet precession , warped disk , and internal helical shock , we suggest that the systematic velocity gradients observed in the bullets result from the rotation of the SVS 13 A jet .
From the SMA CO images , the measured rotation velocities are 11.7–13.7 km s ^ { -1 } for the blueshifted bullet and 4.7 \pm 0.5 km s ^ { -1 } for the redshifted bullet .
The estimated specific angular momenta of the two bullets are comparable to those of dense cores , about 10 times larger than those of protostellar envelopes , and about 20 times larger than those of circumstellar disks .
If the velocity gradients are due to the rotation of the SVS 13 A jet , the significant amount of specific angular momenta of the bullets indicates that the rotation of jets/outflows is a key mechanism to resolve the so-called “ angular momentum problem ” in the field of star formation .
The kinematics of the bullets suggests that the jet launching footprint on the disk has a radius of \sim 7.2–7.7 au , which appears to support the extended disk-wind model .
We note that further observations are needed to comprehensively understand the kinematics of the SVS 13 A jet , in order to confirm the rotation nature of the bullets .