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Abstract

Observations of a number of Class 0/Class I protostars using the Atacama Submillimeter Telescope Experiment (ASTE) have revealed an extended halo of CS (J=7-6) and HCN (J=4-3) molecular line emission, which traces gas of high densities (ncrit~10⁷) and warm temperature (>40K), from up to 4000 AU around the central protostar, including B335, L1551 IRS 5 and L483. These objects also show an interesting common feature: an opposite direction of velocity gradients (along the outflow axis) between the high-density tracer, i.e. CS (J=7-6) and HCN (J=4-3) line emission, and the CO (J=2-1) line emission (ncrit~10⁴) which traces the molecular outflow. In order to study at higher resolution the structure and kinematics and distribution of CS (J=7-6) and to compare that with the CO (J=2-1) lines, we observed one of these objects using radio interferometer. We have mapped the ¹²CO, ¹³CO and C¹⁸O (J=2-1) as well as the CS (J=7-6) line emission from L483 using the Submillimeter Array (SMA). Our observations show two distinct components in both the CS and CO lines: a compact central component exhibiting velocity gradients both perpendicular and parallel to the bipolar molecular outflow, which traces a circumstellar pseudodisk and an extended component elongated along the outflow axis. Intriguingly, the CS (J=7-6) extended component elongated along the outflow direction exhibits a velocity gradient that is opposite to that of the bipolar molecular outflow, traced by the CO (J=2-1) lines. Combination of the CS (J=7-6) SMA and previous ASTE data is also done to better explore the CS (J=7-6) emission on different scale. The results and preliminary interpretation will be given in this presentation.