Proper Motions of the Jets in the Region of HH 30 and HL/XZ Tau: Evidence for a Binary Exciting Source of the HH 30 Jet

Abstract

We present [S II] 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 ~100-300 km s-1 for the HH 30 jet and counterjet and of ~120 km s-1 for the HL Tau jet. Inclination angles with respect to the plane of the sky are 0°-40° for the HH 30 jet and 60° for the HL Tau jet. Comparison with previous observations suggests that most of the jet knots consist of persistent 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 from orbital motion of the jet source around a primary or from 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⊙. In the precession scenario, the mass of the jet source would be ~0.1-1 M⊙, the orbital period <1 yr, and the mass of the companion less than a few times 0.01 M⊙, thus being a substellar object or a giant exoplanet. In both scenarios a binary system with a separation <18 AU (<0.13'') is required. Since the radius of the flared disk observed with the HST is ~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.