2010ApJ...717...58H

The protostellar jet driven by L1448C was observed in the SiO J = 8-7 and CO J = 3-2 lines, and 350 GHz dust continuum at ∼1'' resolution with the Submillimeter Array. A narrow jet from the northern source L1448C(N) was observed in the SiO and the high-velocity CO. The jet consists of a chain of emission knots with an inter-knot spacing of ∼2'' (500 AU) and a semi-periodic velocity variation. These knots are likely to be the internal bow shocks in the jet beam that were formed due to the periodic variation of the ejection velocity with a period of ∼15-20 yr. The innermost pairs of knots, which are significant in the SiO map but barely seen in the CO, are located at ∼1'' (250 AU) from the central source, L1448C(N). Since the dynamical timescale for the innermost pair is only ∼10 yr, SiO may have been formed in the protostellar wind through the gas-phase reaction, or formed on the dust grain and directly released into the gas phase by means of shocks. It is found that the jet is extremely active with a mechanical luminosity of ∼7 L_☉, which is comparable to the bolometric luminosity of the central source (7.5 L_☉). The mass accretion rate onto the protostar derived from the mass-loss rate is ∼10^–5 M_☉/yr. Such a high mass accretion rate suggests that the mass and the age of the central star are 0.03-0.09 M_☉ and (4-12)x10³ yr, respectively, implying that the central star is in the very early stage of protostellar evolution. The low-velocity CO emission delineates two V-shaped shells with a common apex at L1448C(N). The kinematics of these shells are reproduced by the model of a wide-opening angle wind. The co-existence of the highly collimated jets and the wide-opening angle shells can be explained by the "unified X-wind model" in which highly collimated jet components correspond to the on-axis density enhancement of the wide-opening angle wind. The CO J = 3-2 map also revealed the second outflow driven by the southern source L1448C(S) located at ∼8{farcs}3 (2000 AU) from L1448C(N). Although L1448C(S) is brighter than L1448C(N) in the mid-IR bands, the momentum flux of the outflow from L1448C(S) is 2 or 3 orders of magnitude smaller than that of the L1448C(N) outflow. It is likely that the evolution of L1448C(S) has been strongly affected by the powerful outflow from L1448C(N).