L1157-B1激波区的CHESS调查：喷气驱动弓形激波的CO谱特征
The CHESS survey of the L1157-B1 shock region: CO spectral signatures of jet-driven bowshocks
摘要：
Herschel前所未有的灵敏度加上HIFI光谱仪的高分辨率，可以在比目前更高的激发范围内研究分子流出中的强度-速度关系I（v）。在CHESS Key计划的过程中，我们用HIFI观测到了L1157-B1明亮弓形激波区的J=5-4和J=16-15之间的CO转动跃迁，用IRAM-30 m和CSO望远镜观测到了J=1-0、2-1和3-2之间的CO转动跃迁。我们发现所有的谱线轮廓I_{CO}（v）都能很好地用三个指数律exp（-）的线性组合拟合|v/v_0| v_0= 12.5，4.4和2.5km/s时的平均速度。当J_up > 13时，第一种组分在CO发射中占主导地位，同时也是SiO和H_2O的高激发谱线。第二个分量在3 < J_up < 10时占主导，第三个分量在J_up < 2时占主导。我们表明，这些指数是准等温冲击气体成分的签名：对L1157-B1弓形激波（T= 210 K），与B1（T= 64 K）和老腔L1157-B2（T= 23 K），分别与流出腔的壁射流的影响。在大速度梯度近似下对CO谱线通量的分析进一步表明，在J=20之前，发射来自接近LTE的致密气体（n（H2）> 1 e5 - 1 e6 cm-3）。我们发现，在各种其他分子外流中观察到的CO J=2-1强度-速度关系令人满意地符合类似的指数律，这可能是它们的夹带过程的重要线索。
英文摘要：
The unprecedented sensitivity of Herschel coupled with the high resolution of the HIFI spectrometer permits studies of the intensity-velocity relationship I(v) in molecular outflows, over a higher excitation range than possible up to now. In the course of the CHESS Key Program, we have observed toward the bright bowshock region L1157-B1 the CO rotational transitions between J=5-4 and J=16-15 with HIFI, and the J=1-0, 2-1 and 3-2 with the IRAM-30m and the CSO telescopes. We find that all the line profiles I_{CO}(v) are well fit by a linear combination of three exponential laws exp(-|v/v_0|) with v_0= 12.5, 4.4 and 2.5km/s. The first component dominates the CO emission at J_up > 13, as well as the high-excitation lines of SiO and H2O. The second component dominates for 3 < J_up < 10 and the third one for J_up < 2. We show that these exponentials are the signature of quasi-isothermal shocked gas components: the impact of the jet against the L1157-B1 bowshock (T= 210K), the walls of the outflow cavity associated with B1 (T= 64K) and the older cavity L1157-B2 (T= 23K), respectively. Analysis of the CO line flux in the Large-Velocity Gradient approximation further shows that the emission arises from dense gas (n(H2) > 1e5-1e6 cm-3) close to LTE up to J=20. We find that the CO J=2-1 intensity-velocity relation observed in various other molecular outflows is satisfactorily fit by similar exponential laws, which may hold an important clue to their entrainment process.
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