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Context. Kinematical and time variability studies of protostellar jets are fundamental for understanding the dynamics and the physics of these objects. Such studies remain very sporadic, since they require long baselines before they can be accomplished.

Aims.We present a detailed study of the infrared line emission (1–200 μm) in the Herbig-Haro object HH54. Our database comprises: high- (R~ 9000) and low- (R~ 600) resolution spectroscopic data in the near-infrared band (1–2.5 μm); mid-infrared spectrophotometric images (5–12 μm); and, far-IR (45–200 μm, R~ 200) spectra acquired with the ISO satellite. As a result, we provide the detection of and the absolute fluxes for more than 60 molecular features (mainly from H2in the near- and mid-infrared and from H2O, CO and OH in the far-infrared) and 23 ionic lines.

We present an in-depth near-IR analysis of a sample of H2outflows from young embedded sources to compare the physical properties and cooling mechanisms of the different flows. The sample comprises 23 outflows driven by Class 0 and I sources having low-intermediate luminosity. We have obtained narrow band images in H22.12 μm and [$\ion{Fe}{ii}$] 1.64 μm and spectroscopic observations in the range 1-2.5 μm. From [$\ion{Fe}{ii}$] images we detected spots of ionized gas in ~74% of the outflows which in some cases indicate the presence of embedded HH-like objects. H2line ratios have been used to estimate the visual extinction and average temperature of the molecular gas. Avvalues range from ~2 to ~15 mag; average temperatures range between ~2000 and ~4000 K. In several knots, however, a stratification of temperatures is found with maximum values up to 5000 K. Such a stratification is more commonly observed in those knots which also show [$\ion{Fe}{ii}$] emission, while a thermalized gas at a single temperature is generally found in knots emitting only in molecular lines. Combining narrow band imaging (H2, 2.12 μm and [$\ion{Fe}{ii}$], 1.64 μm) with the parameters derived from the spectroscopic analysis, we are able to measure the total luminosity of the H2and [$\ion{Fe}{ii}$] shocked regions ($L_{\rm H_2}$and $L_{[\ion{Fe}{ii}]}$) in each flow. H2is the major NIR coolant with an average $L_{\rm H_2}$/$L_{[\ion{Fe}{ii}]}$ratio of ~102. We find that ~83% of the sources have a $L_{\rm H_2}$/Lbolratio ~0.04, irrespective of the Class of the driving source, while a smaller group of sources (mostly Class I) have $L_{\rm H_2}$/Lbolan order of magnitude smaller. Such a separation reveals the non-homogeneous behaviour of Class I, where sources with very different outflow activity can be found. This is consistent with other studies showing that among Class I one can find objects with different accretion properties, and it demonstrates that the H2power in the jet can be a powerful tool to identify the most active sources among the objects of this class.

Context. Protostellar jets from intermediate- and high-mass protostars provide an excellent opportunity to understand the mechanisms responsible for intermediate- and high-mass star-formation. A crucial question is if they are scaled-up versions of their low-mass counterparts. Such high-mass jets are relatively rare and, usually, they are distant and highly embedded in their parental clouds. The IRAS?20126+4104 molecular jet, driven by a 104?L?protostar, represents a suitable target to investigate.Aims. We present here an extensive analysis of this protostellar jet, deriving the kinematical, dynamical, and physical conditions of the H2gas along the flow.Methods. The jet was investigated by means of near-IR H2and [Feii] narrow-band imaging, high-resolution spectroscopy of the 1?0?S(1) line (2.12??m), NIR (0.9?2.5??m) low-resolution spectroscopy, along with ISO-SWS and LWS spectra (from 2.4 to 200??m). Results. The flow shows a complex morphology. In addition to the large-scale jet precession presented in previous studies, we detect a small-scale wiggling close to the source, which may indicate the presence of a multiple system. The peak radial velocities of the H2knots range from ?42 to ?14?km?s-1in the blue lobe, and from ?8 to 47?km?s-1in the red lobe. The low-resolution spectra are rich in H2emission, and relatively faint [Feii] (NIR), [Oi] and [Cii] (FIR) emission is observed in the region close to the source. A warm H2gas component has an average excitation temperature that ranges between 2000?K and 2500?K. Additionally, the ISO-SWS spectrum reveals a cold component (520?K) that strongly contributes to the radiative cooling of the flow and plays a major role in the dynamics of the flow. The estimated LH2of the jet is 8.2 ?0.7?L?, suggesting that IRAS?20126+4104 has a significantly increased accretion rate compared to low-mass YSOs. This is also supported by the derived mass flux rate from the H2lines (Mout(H2)?7.5?10-4?M??yr-1). The comparison between the H2and the outflow parameters strongly indicates that the jet is driving the outflow, at least partially. As already found for low-mass protostellar jets, the measured H2outflow luminosity is tightly related to the source bolometric luminosity. Conclusions. As for a few other intermediate- and high-mass protostellar jets in the literature, we conclude that IRAS?20126+4104 jet is a scaled-up version of low-mass protostellar counterparts.

Context.We present the results of the analysis of low-resolution optical-near IR spectroscopy (0.6–2.4 μm) of a sample (47 sources) of Class I and Class II young stellar objects in the Chamaeleon I and II star-forming clouds. These data are part of the POISSON project (Protostellar Optical-Infrared Spectral Survey On NTT).

Context.Most of our knowledge about star formation is based on studies of low-mass stars, whereas very little is known about the properties of the circumstellar material around young and embedded intermediate-mass T Tauri stars (IMTTSs) mostly because they are rare, typically more distant than their lower mass counterparts, and their nearby circumstellar surroundings are usually hidden from us.

Context.Strong outbursts in very young and embedded protostars are rare and not yet fully understood. They are believed to originate from an increase in the mass accretion rate (Ṁacc) onto the source.