The structure of the Cepheus E protostellar outflow: The jet, the bowshock, and the cavity⋆
Univ. Grenoble Alpes, IPAG, 38000
2 CNRS, IPAG, 38000 Grenoble, France
3 LERMA, Observatoire de Paris, PSL Research University, CNRS, UMR 8112, 75014 Paris, France
4 Sorbonne Universités, UPMC Univ. Paris 6, UMR 8112, LERMA, 75005 Paris, France
5 INAF, Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
6 Thüringer Landessternwarte, Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
7 Institut de Radioastronomie Millimétrique, Domaine Universitaire, 38406 St.-Martin-d’Hères, France
8 Instituto Nacional de Astrofísica, Optica y Electrónica, Luis E. Erro 1, Tonantzintla, CP 72840 Puebla, Mexico
9 Max Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
10 INAF – Istituto di Astrofisica e Planetologia Spaziali, via del Fosso del Cavaliere 100, 00133 Roma, Italy
Accepted: 19 June 2015
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 = 500–1500K, 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.
Key words: stars: formation / ISM: individual objects: Cep E / ISM: kinematics and dynamics / shock waves / infrared: ISM / ISM: jets and outflows
Appendices are available in electronic form at http://www.aanda.org
© ESO, 2015