Modeling the early mass ejection in jet-driven protostellar outflows: Lessons from Cep E

Abstract

Context. Protostellar jets and outflows are an important agent of star formation as they carry away a fraction of momentum and energy, which is needed for gravitational collapse and protostellar mass accretion to occur. Aims. Our goal is to provide constraints on the dynamics of the inner protostellar environment from the study of the outflow-jet propagation away from the launch region. Methods. We have used the axisymmetric chemo-hydrodynamical code WALKIMYA-2D to numerically model and reproduce the physical and CO emission properties of the jet-driven outflow from the intermediate-mass protostar CepE-mm, which was observed at ~800 au resolution in the CO J = 2−1 line with the IRAM interferometer. Our simulations take into account the observational constraints available on the physical structure of the protostellar envelope. Results. WALKIMYA-2D successfully reproduces the main qualitative and quantitative features of the Cep E outflow and the jet kinematics, naturally accounting for their time variability. Signatures of internal shocks are detected as knots along the jet. In the early times of the ejection process, the young emitted knots interact with the dense circumstellar envelope through high-velocity, dissociative shocks, which strongly decrease the CO gas abundance in the jet. As time proceeds, the knots propagate more smoothly through the envelope and dissociative shocks disappear after ~103 yr. The distribution of CO abundance along the jet shows that the latter bears memory of the early dissociative phase in the course of its propagation. Analysis of the velocity field shows that the jet material mainly consists of gas entrained from the circumstellar envelope and accelerated away from the protostar at 700 au scale. As a result, the overall jet mass-loss rate appears higher than the actual mass-ejection rate by a factor ~3. Conclusions. Numerical modeling of the Cep E jet-driven outflow and comparison with the CO observations have allowed us to peer into the outflow formation mechanism with unprecedented detail and to retrieve the history of the mass-loss events that have shaped the outflow.

Investigating Protostellar Accretion-driven Outflows across the Mass Spectrum: JWST NIRSpec Integral Field Unit 3–5 μm Spectral Mapping of Five Young Protostars

“…In most cavities traced by the continuum, we do not find enhanced emission along the cavity wall in the S(11) line, as would be expected for shocks owing to a wide-angle wind colliding with the cavity walls. Instead, we often find narrow shells of H 2 that appear similar to the bow shocks and wakes created by internal working surfaces within jets (Tafalla et al 2017;Tabone et al 2018;Rabenanahary et al 2022;Rivera-Ortiz et al 2023). The coincidence of the apex of the IRAS 16253 shell with the [Fe II]/Brα knot supports this picture.…”

“…The knots trace shocks within the jets that likely originate in internal working surfaces, layers of shock-heated gas resulting from higher-velocity material colliding with slower-moving material in the jet (e.g., Schwartz 1983;Raga & Kofman 1992;Reipurth & Heathcote 1992;Suttner et al 1997;Völker et al 1999;Nisini et al 2002). Models and simulations invoking a jet with an oscillating velocity but a constant mass flow rate produce chains of such knots (Raga et al 1990;Raga & Kofman 1992;Rabenanahary et al 2022;Rivera-Ortiz et al 2023).…”

“…Despite the importance of infall and outflow for determining the masses of stars and the star formation efficiency, the processes by which outflows clear cavities and entrain gas are still debated. Cavities can be carved by high-velocity X-winds, high-velocity pulsed jets, or lower-velocity disk winds (e.g., Machida & Hosokawa 2013;Shang et al 2020;Ray & Ferreira 2021;Rabenanahary et al 2022;Rivera-Ortiz et al 2023). The IPA program will search for signatures of accretion in emission and absorption lines, map the flows of gas inside outflow cavities using shock tracers, and examine the interaction between outflows and the surrounding cavity (Narang et al 2024;Rubinstein et al 2023a;D.…”

Shedding Light on the Ejection History of Molecular Outflows: Multiple Velocity Modes and Precession

“…The physical processes in the molecular outflow of core MM1#8 could be different from those of the intermediatemass Cepheus E core, which was recently studied with CO observations and numerical simulations (de Schutzer et al 2022;Rivera-Ortiz et al 2023). Rivera-Ortiz et al (2023) showed that one-velocity ejection variations successfully reproduce the observed features, especially the bimodal distribution of the dynamical timescales of the knots. On the contrary, we showed in this work that a two-velocity ejection mode is necessary to reproduce the observed velocity variations among the knots.…”

“…Rabenanahary et al (2022) compared simulations of an outflow driven by a pulsed jet and observations in CARMA-7 by Plunkett et al (2015). Rivera-Ortiz et al (2023) carried out simulations of a jet aimed at reproducing the Cepheus E outflow observed by de Schutzer et al (2022).…”