We present [ SII ] images of the HH 30 and HL/XZ Tau region obtained at two epochs , as well as long-slit optical spectroscopy of the HH 30 jet .
We measured proper motions of \sim 100–300 km s ^ { -1 } for the HH 30 jet and counterjet , and of \sim 120 km s ^ { -1 } for the HL Tau jet .
Inclination angles with respect to the plane of the sky are 0 ^ { \circ } – 40 ^ { \circ } for the HH 30 jet and 60 ^ { \circ } for the HL Tau jet .
Comparison with previous observations suggests that most of the jet knots consist of persisting structures .
Also , we corroborate that the HH 30-N knots correspond to the head of the HH 30 jet .
The overall HH 30 jet structure can be well described by a wiggling ballistic jet , arising either by the orbital motion of the jet source around a primary or by precession of the jet axis because of the tidal effects of a companion .
In the first scenario , the orbital period would be 53 yr and the total mass 0.25-2 M _ { \odot } .
In the precession scenario , the mass of the jet source would be \sim 0.1 –1 M _ { \odot } , the orbital period < 1 yr , and the mass of the companion less than a few times 0.01 ~ { } M _ { \odot } , thus being a substellar object or a giant exoplanet .
In both scenarios a binary system with a separation < 18 AU ( < 0 \hbox to 0.0 pt { . } ^ { \prime \prime } 13 ) is required .
Since the radius of the flared disk observed with the HST is \sim 250 AU , we conclude that this disk appears to be circumbinary rather than circumstellar , suggesting that the search for the collimating agent of the HH 30 jet should be carried out at much smaller scales .