NIR spectroscopic survey of protostellar jets in the star-forming region IC 1396N^★,★★

¹ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: fabrizio.massi@inaf.it
² Departament de Física Quàntica i Astrofísica, Institut de Ciències del Cosmos, Universitat de Barcelona, IEEC-UB, Martí i Franquès, 1, 08028 Barcelona, Spain
³ Institut de Ciències de l’Espai (ICE), CSIC, Carrer de Can Magrans, s/n, 08193 Cerdanyola del Vallès, Catalonia, Spain
⁴ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Catalonia, Spain

Received: 16 March 2022
Accepted: 5 May 2022

Abstract

Context. The bright-rimmed cloud IC 1396N, associated with an intermediate-mass star-forming region, hosts a number of CO, molecular hydrogen, and Herbig-Haro (HHs) outflows powered by a set of millimetre compact sources.

Aims. The aim of this work is to characterise the kinematics and physical conditions of the H₂ emission features spread throughout the IC 1396N region. The features appear as chains of knots with a jet-like morphology and trace different H₂ outflows. We also obtain further information about (and an identification of) the driving sources.

Methods. Low-resolution, long-slit near-infrared spectra were acquired with the NICS camera at the TNG telescope, using grisms KB (R ~ 1200), HK, and JH (R ~ 500). Several slit pointings and position angles were used throughout the IC 1396N region in order to sample a number of the H₂ knots that were previously detected in deep H₂ 2.12 μm images.

Results. The knots exhibit rich ro–vibrational spectra of H₂, consistent with shock-excited excitation, from which radial velocities and relevant physical conditions of the IC 1396N H₂ outflows were derived. These also allowed estimating extinction ranges towards several features. [Fe ii] emission was only detected towards a few knots that also display unusually high H₂ 1–0 S(3)/S(1) flux ratios. The obtained radial velocities confirm that most of the outflows are close to the plane of the sky. Nearby knots in the same chain often display different radial velocities, both blue–shifted and red–shifted, which we interpret as due to ubiquitous jet precession in the driving sources or the development of oblique shocks. One of the chains (strand A, i.e. knots A1 to A15) appears as a set of features trailing a leading bow-shock structure consistent with the results of 3D magneto-hydrodynamical models. The sides of the leading bow shock (A15) exhibit different radial velocities. We discuss possible explanations. Our data cannot confirm whether strands A and B have both originated in the intermediate mass young stellar object [BGE2002] BIMA 2 because a simple model of a precessing jet cannot account for their locations.

Conclusions. Near-infrared spectroscopy has confirmed that most of the H₂ ro-vibrational emission in IC 1396N is shock-excited rather than uv-excited in photon-dominated regions. It has shown a complex kinematical structure in most strands of emitting knots as well.