摘要
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″ (500AU) 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 15-20yr. The innermost pairs of knots, which are significant in the SiO map but barely seen in the CO, are located at 1″ (250AU) from the central source, L1448C(N). Since the dynamical timescale for the innermost pair is only 10yr, 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 -1 . 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)×10 3 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 83 (2000AU) 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). © 2010. The American Astronomical Society. All rights reserved..