THE COUNTERJET OF HH 30: NEW LIGHT ON ITS BINARY DRIVING SOURCE

We present new [S II] images of the Herbig-Haro (HH) 30 jet and counterjet observed in 2006, 2007, and 2010 that, combined with previous data, allowed us to measure with improved accuracy the positions and proper motions of the jet and counterjet knots. Our results show that the motion of the knots is essentially ballistic, with the exception of the farthest knots, which trace the large-scale 'C'-shape bending of the jet. The observed bending of the jet can be produced by a relative motion of the HH 30 star with respect to its surrounding environment, caused either by a possible proper motion of the HH 30 star, or by the entrainment of environment gas by the red lobe of the nearby L1551-IRS5 outflow. Alternatively, the bending can be produced by the stellar wind from a nearby classical T Tauri star, identified in the Two Micron All Sky Survey catalog as J04314418+181047. The proper motion velocities of the knots of the counterjet show more variations than those of the jet. In particular, we identify two knots of the counterjet that have the same kinematic age but whose velocities differ by almost a factor of two. Thus, it appears from our observations that counterjet knots launched simultaneously can be ejected with very different velocities. We confirm that the observed wiggling of the jet and counterjet arises from the orbital motion of the jet source in a binary system. Precession, if present at all, is of secondary importance in shaping the jet. We derive an orbital period of τo = 114 ± 2 yr and a mass function of mμ3c = 0.014 ± 0.006 M☉. For a mass of the system of m = 0.45 ± 0.04 M☉ (the value inferred from observations of the CO kinematics of the disk), we obtain a mass of mj = 0.31 ± 0.04 M☉ for the jet source, a mass of mc = 0.14 ± 0.03 M☉ for the companion, and a binary separation of a = 18.0 ± 0.6 AU. This binary separation coincides with the value required to account for the size of the inner hole observed in the disk, which has been attributed to tidal truncation in a binary system.