Observation of Class 0 Protostars: L1157-mm and L1448C
| Autor: | Wen-Cheng Wu, 吳文正 |
|---|---|
| Rok vydání: | 2013 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 101 We present molecular lines and continuum images of two low-mass class 0 protostars, L1157mm and L1448C obtained by the Submillimeter Array (SMA). The angular resolution was 3′′ ∼ 5′′, which corresponds to 650 ∼ 1500 AU. The 12CO(2-1), 13CO(2-1), C18O(2-1), CS (7-6) and H2CO (51;5-41;4) lines were detected in both sources. The 12CO emission with low velocity ( V ≤ ± 6 km s−1 in L1157,and ≤ ± 20 km s−1 in L1448C) show that the outflow lobes near the protostars have a V-shaped structure with an opening angle of 30◦ ∼40◦. The morphologies and kinematics of the low velocity shells are reproduced by the model of wide-opening angle wind. In addition to the V-shaped lobes, a narrow jet with extremely high velocity (EHV) was observed in the L1448C outflow. The EHV jet in the L1448C outflow was also traced by the SiO (8-7) and SO (56-45) lines. The appearance of this EHV jet in SiO and SO suggests that there are shocks in the jet beam, representing the internal working surfaces. In the L1157 outflow, the 12CO intensity is significantly enhanced in the eastern wall of the southern lobe and the western wall of the northern lobe. This suggests that the recent mass ejection of the L1157 outflow is in the NW-SE direction. The position angle of this recent ejection event can be explained by the precession model with a precession angle of 15◦. The C18O(2-1), CS (7-6) and H2CO (51;5-41;4) emission show compact structures around the central stars. These dense gas envelopes around L1157-mm and L1448C are strongly affected by the outflow. In L1448C, these lines show elongated structures along the outflow axis, and velocity gradients with the same sense of 12CO outflow. In L1157, the C18O shows the same velocity gradient as the outflow, while the CS and H2CO exhibit the opposite velocity gradient. The kinematic structure of the L1157 envelope is explained if the envelope had cavities with wide opening angles at their bases. Our results support the idea that the outflows play key roles in changing the physical condition of circumstellar envelopes. On the other hand, the C18O shows a velocity gradient that is perpendicular to the outflow axis in both sources, suggesting that the envelopes around the protostars are rotating. The estimated specific angular momenta are 2.17 × 10−4 km s−1 pc and 5.5 × 10−3 km s−1 pc for L1157 and L1448C, respectively. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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