The structure of the Cepheus E protostellar outflow: The jet, the bowshock, and the cavity^⋆

¹ Univ. Grenoble Alpes, IPAG, 38000 Grenoble, France
e-mail: Bertrand.Lefloch@obs.ujf-grenoble.fr
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

Received: 15 December 2014
Accepted: 19 June 2015

Abstract

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 T_kin = 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 (T_kin = 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 T_kin = 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 T_kin = 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 T_kin ≈ 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.