The structure of the Cepheus E protostellar outflow: The jet, the bowshock, and the cavity
The structure of the Cepheus E protostellar outflow: The jet, the bowshock, and the cavity
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DOI：
10.1051/0004-6361/201425521
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发表时间：
2015-09
影响因子：
6.5
通讯作者：
B. Lefloch;A. Gusdorf;C. Codella;J. Eislöffel;R. Neri;A. Gómez-Ruiz;R. Güsten;S. Leurini;C. Risacher;M. Benedettini
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作者：
B. Lefloch;A. Gusdorf;C. Codella;J. Eislöffel;R. Neri;A. Gómez-Ruiz;R. Güsten;S. Leurini;C. Risacher;M. Benedettini
上下文。原恒星流出物是恒星形成过程的重要组成部分。然而，在温暖的流出气体的物理条件仍然知之甚少。目标。我们对中质量0级原恒星Cep E-mm的流出进行了多跃迁、高光谱分辨率的CO研究。目的是确定流出的结构，并约束各组分的物理条件，以便了解质量损失现象的起源。方法。我们用SOFIA/GREAT在高光谱分辨率下观测到了J = 12-11、J = 13-12和J = 16-15的CO谱线，用HIFI/Herschel观测到了J = 5-4、J = 9-8和J = 14-13的CO谱线，这些CO谱线指向了HH377尾部弓形激波在南部流出叶的位置。这些观测结果与IRAM 30 m望远镜（J = 1 - 0,2 - 1）、Plateau de Bure干涉仪（J = 2-1）和James Clerk Maxwell望远镜（J = 3-2, 4-3）获得的CO跃迁图相辅相成。结果。我们确定了原恒星流出流的三个主要组成部分：喷流、空腔和弓形激波，它们的典型尺寸分别为1.7 “ × 21 ”、4.5 “和22 ” × 10 "。在射流中，低焦CO谱线的发射以Tkin = 80 ~ 100 K的气体层为主，柱密度N(CO) = 9 × 1016 cm−2，密度N(H2) =(0.5−1)× 105 cm−3；高焦距CO谱线的发射来自温度较高（Tkin = 400-750 K）、密度较高(n（H2) =(0.5−1)× 106 cm−3）、柱密度较低（n(CO) = 1.5× 1016 cm−2）的气体组分。同样，在流出腔中，检测到两种成分：低j谱线的发射主要由柱密度N(CO) = 7 × 1017 cm−2 (Tkin = 55-85 K，密度在（1−8）× 105 cm−3范围内的气体层主导；高j谱线的发射主要是热的、密度较大的气体层，Tkin = 500-1500 K, n(H2) =(1−5)× 106 cm−3,n(CO) = 6 × 1016 cm−2。在高激发态气体组分中发现了温度梯度作为速度的函数。在末端弓激波HH377中，我们检测到中等激发气体，温度范围为Tkin≈400-500 K，密度n(H2)（1−2）× 106 cm−3，柱密度n(CO) = 1017 cm−2。在射流中带走的动量和在夹带的周围介质中带走的动量是相似的。与时间相关激波模型的比较表明，射流中的热气体发射是由一个年龄为220-740年的磁化激波在密度为n(H2) =(0.5−1)× 105 cm−3的介质中以20-30 km s−1的速度传播的，这与大块物质的情况一致。结论。Cep E原恒星外流似乎是一个令人信服的案例射流弓形激波驱动的外流。我们的观测追踪了原恒星喷流最近对周围云的影响，产生了一个非静止的磁化激波，它驱动了一个流出腔的形成。
Context. Protostellar outflows are a crucial ingredient of the star-formation process. However, the physical conditions in the warm outflowing gas are still poorly known. Aims. We present a multi-transition, high spectral resolution CO study of the outflow of the intermediate-mass Class 0 protostar Cep E-mm. The goal is to determine the structure of the outflow and to constrain the physical conditions of the various components in order to understand the origin of the mass-loss phenomenon. Methods. We have observed the J = 12–11, J = 13–12, and J = 16–15 CO lines at high spectral resolution with SOFIA/GREAT and the J = 5–4, J = 9–8, and J = 14–13 CO lines with HIFI/Herschel towards the position of the terminal bowshock HH377 in the southern outflow lobe. These observations were complemented with maps of CO transitions obtained with the IRAM 30 m telescope (J = 1–0, 2–1), the Plateau de Bure interferometer (J = 2–1), and the James Clerk Maxwell Telescope (J = 3–2, 4–3). Results. We identify three main components in the protostellar outflow: the jet, the cavity, and the bowshock, with a typical size of 1.7′′ × 21′′, 4.5′′, and 22′′ × 10′′, respectively. In the jet, the emission from the low-J CO lines is dominated by a gas layer at Tkin = 80–100 K, column density N(CO) = 9 × 1016 cm−2, and density n(H2) = (0.5−1) × 105 cm−3; the emission of the high-J CO lines arises from a warmer (Tkin = 400–750 K), denser (n(H2) = (0.5−1)× 106 cm−3), lower column density (N(CO) = 1.5× 1016 cm−2) gas component. Similarly, in the outflow cavity, two components are detected: the emission of the low-J lines is dominated by a gas layer of column density N(CO) = 7 × 1017 cm−2 at Tkin = 55–85 K and density in the range (1−8) × 105 cm−3; the emission of the high-J lines is dominated by a hot, denser gas layer with Tkin = 500–1500 K, n(H2) = (1−5) × 106 cm−3, and N(CO) = 6 × 1016 cm−2. A temperature gradient as a function of the velocity is found in the high-excitation gas component. In the terminal bowshock HH377, we detect gas of moderate excitation, with a temperature in the range Tkin ≈ 400–500 K, density n(H2) (1−2) × 106 cm−3 and column density N(CO) = 1017 cm−2. The amounts of momentum carried away in the jet and in the entrained ambient medium are similar. Comparison with time-dependent shock models shows that the hot gas emission in the jet is well accounted for by a magnetized shock with an age of 220–740 yr propagating at 20–30 km s−1 in a medium of density n(H2) = (0.5−1) × 105 cm−3, consistent with that of the bulk material. Conclusions. The Cep E protostellar outflow appears to be a convincing case of jet bowshock driven outflow. Our observations trace the recent impact of the protostellar jet into the ambient cloud, produing a non-stationary magnetized shock, which drives the formation of an outflow cavity.