SOLIS

XVI. Mass ejection and time variability in protostellar outflows: Cep E

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
e-mail: andre.schutzer@univ-grenoble-alpes.fr
² Laboratoire de Physique de l’ENS, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, 75005 Paris, France
³ Observatoire de Paris, PSL University, Sorbonne Université, LERMA, 75014 Paris, France
⁴ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
⁵ Department of Astronomy, The University of Texas at Austin, 2500 Speedway, Austin, TX 78712, USA
⁶ Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint-Martin-D’Hères, France
⁷ INAF, Osservatorio Astrofísico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁸ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁹ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
¹⁰ IGN, Observatorio Astronómico Nacional, Calle Alfonso XII, 28004 Madrid, Spain
¹¹ Dipartimento di Chimica, Biologia e Biotecnologie, Via Elce di Sotto 8, 06123 Perugia, Italy
¹² Dipartimento di Chimica “G. Ciamician” via F. Selmi 2, 40126 Bologna, Italy
¹³ Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
¹⁴ CNRS, IRAP, 9 Av. Colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
¹⁵ LERMA, Université de Cergy-Pontoise, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Université, UPMC, Univ. Paris 06, 95000 Cergy Pontoise, France
¹⁶ Departament de Química, Universitat Autónoma de Barcelona, 08193 Bellaterra, Catalonia, Spain
¹⁷ Centro de Astrobiología (CSIC, INTA), Ctra. de Ajalvir, km. 4, Torrejón de Ardoz, 28850 Madrid, Spain
¹⁸ University of AL-Muthanna, College of Science, Physics Department, AL-Muthanna, Iraq
¹⁹ Department of Physics, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
²⁰ Ural Federal University, 620002, 19 Mira street, Yekaterinburg, Russia
²¹ The Institute of Physical and Chemical Research (RIKEN), 2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan
²² Univ. Rennes, CNRS, IPR (Institut de Physique de Rennes) – UMR 6251, 35000 Rennes, France
²³ ESO, Karl Schwarzchild Srt. 2, 85478 Garching bei München, Germany
²⁴ Aix-Marseille Université, PIIM UMR-CNRS 7345, 13397 Marseille, France
²⁵ Università degli Studi di Torino, Dipartimento Chimica Via Pietro Giuria 7, 10125 Torino, Italy

Received: 16 December 2021
Accepted: 8 March 2022

Abstract

Context. Protostellar jets are an important agent of star formation feedback, tightly connected with the mass-accretion process. The history of jet formation and mass ejection provides constraints on the mass accretion history and on the nature of the driving source.

Aims. We characterize the time-variability of the mass-ejection phenomena at work in the class 0 protostellar phase in order to better understand the dynamics of the outflowing gas and bring more constraints on the origin of the jet chemical composition and the mass-accretion history.

Methods. Using the NOrthern Extended Millimeter Array (NOEMA) interferometer, we have observed the emission of the CO 2–1 and SO N_J = 5₄–4₃ rotational transitions at an angular resolution of 1.0″ (820 au) and 0.4″ (330 au), respectively, toward the intermediate-mass class 0 protostellar system Cep E.

Results. The CO high-velocity jet emission reveals a central component of ≤400 au diameter associated with high-velocity molecular knots that is also detected in SO, surrounded by a collimated layer of entrained gas. The gas layer appears to be accelerated along the main axis over a length scale δ₀ ~ 700 au, while its diameter gradually increases up to several 1000 au at 2000 au from the protostar. The jet is fragmented into 18 knots of mass ~10⁻³ M_⊙, unevenly distributed between the northern and southern lobes, with velocity variations up to 15 km s⁻¹ close to the protostar. This is well below the jet terminal velocities in the northern (+ 65 km s⁻¹) and southern (−125 km s⁻¹) lobes. The knot interval distribution is approximately bimodal on a timescale of ~50–80 yr, which is close to the jet-driving protostar Cep E-A and ~150–20 yr at larger distances >12″. The mass-loss rates derived from knot masses are steady overall, with values of 2.7 × 10⁻⁵ M_⊙ yr⁻¹ and 8.9 × 10⁻⁶ M_⊙ yr⁻¹ in the northern and southern lobe, respectively.

Conclusions. The interaction of the ambient protostellar material with high-velocity knots drives the formation of a molecular layer around the jet. This accounts for the higher mass-loss rate in the northern lobe. The jet dynamics are well accounted for by a simple precession model with a period of 2000 yr and a mass-ejection period of 55 yr.