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Abstract. As part of a 1-2.5 µm spectroscopic survey of jets and molecular outflows, we present the spectra of three Herbig Haro chains (HH111, HH240/241, HH120) characterized by strong emission from several Fe  transitions originating from the first 13 fine structure levels. Such emission is correlated with optical S  emission and appears to decrease moving away from the driving source. From the analysis of the Fe  lines we have derived electron densities values in the range 3 × 10 3 -2 × 10 4 cm −3 , which are systematically larger than those inferred from optical S  line ratios. We suggest that Fe  lines, having critical densities higher than the optical S  transitions, trace either regions of the post-shock cooling layers with higher compression, or a section of the jet axis at a higher degree of ionization. Strong H 2 emission lines are also detected along the three flows and their analysis indicates that a combination of different shocks can be responsible for their excitation in the different objects. Consequently the Fe  line emission, which requires the presence of fast dissociative shocks, is completely independent from the excitation mechanism giving rise to the molecular emission. In addition to the Fe  and H 2 lines, emission from other species such as C , S , N  as well as recombination lines from the Paschen series are detected and have been used as a reference to infer the gas-phase iron abundance in the observed HH objects. We estimate a grain destruction efficiency of about 30-60%: the highest value is found for HH240A, which also shows the highest degree of excitation among the observed objects.

We present an in-depth near-IR analysis of a sample of H 2 outflows 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 H 2 2.12 µm and [Fe ii] 1.64 µm and spectroscopic observations in the range 1−2.5 µm. From [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. H 2 line ratios have been used to estimate the visual extinction and average temperature of the molecular gas. A v values 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 [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 (H 2 , 2.12 µm and [Fe ii], 1.64 µm) with the parameters derived from the spectroscopic analysis, we are able to measure the total luminosity of the 2 . We find that ∼83% of the sources have a L H 2 /L bol ratio ∼0.04, irrespective of the Class of the driving source, while a smaller group of sources (mostly Class I) have L H 2 /L bol an 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 H 2 power in the jet can be a powerful tool to identify the most active sources among the objects of this class.

Abstract. Near IR spectra at low (R ∼ 800) and medium (R ∼ 9000) resolution, obtained with ISAAC at VLT, have been used to pose constraints on the evolutionary state and accretion properties of a sample of five embedded YSOs located in the R CrA core. This sample includes three Class I sources (HH100 IR, IRS2 and IRS5), and two sources with NIR excesses (IRS6 and IRS3). IRS5 and IRS6 have been discovered to be binaries with a separation between the two components of 78 and 97 AU, respectively. Absorption lines, typical of late-type photospheres, have been detected in the medium resolution spectra of all the observed targets, including HH100 IR and IRS2 which have high values of infrared continuum veiling (r K = 6 and 3, respectively). These two sources also present low resolution spectra rich in emission lines (HI, CO and plenty of other permitted lines from neutral atoms) likely originating in the disk-star-wind connected regions. Among the features observed in HH100 IR and IRS2, Na I at 2.205 µm and CO at 2.3 µm, which are more commonly used for stellar classification, are detected in emission instead of absorption. Several strong photospheric lines which lie around 2.12 and 2.23 µm and whose ratio is sensitive to both effective temperature and gravity are proposed as independent diagnostic tools for this type of sources. We derived spectral types, veiling and stellar luminosity for the five observed sources, which in turn have been used to infer their mass (ranging between 0.3−1.2 M ) and age (between 10 5 and 10 6 yr) adopting pre-main sequence evolutionary tracks. We find that in HH100 IR and IRS2 most of the bolometric luminosity is due to accretion (L acc /L bol ∼ 0.8 and 0.6 respectively), while the other three investigated sources, including the Class I object IRS5a, present low accretion activity (L acc /L bol < 0.2). Mass accretion rates of the order of 2 × 10 −6 and 3 × 10 −7 M yr −1 are derived for HH100 IR and IRS2, respectively, i.e. higher by an order of magnitude than the average values derived for T Tauri stars. We observe a general correlation between the accretion luminosity, the IR veiling and the emission line activity of the sources. In particular, we find that the correlation between L acc and L Brγ , previously reported for optical T Tauri stars, can be extended to the embedded sources, up to at least one order of magnitude larger line luminosity. A correlation between the accretion activity and the spectral energy distribution slope is recognizable with the notable exception of IRS5a. Our analysis therefore shows how the definition of the evolutionary stage of deeply embedded YSOs by means of IR colors needs to be refined.

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