Molecular jets driven by high-mass protostars: a detailed study of the IRAS 20126+4104 jet

Abstract

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 10 4 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 H 2 gas along the flow. Methods. The jet was investigated by means of near-IR H 2 and [Fe ii] narrow-band imaging, high-resolution spectroscopy of the 1-0 S(1) line (2.12 μm), NIR (0.9-2.5 μm) low-resolution spectroscopy, along with ISO-SWS and LWS spectra (from 2.4 to 200 μm). 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 H 2 knots range from -42 to -14 km s −1 in the blue lobe, and from -8 to 47 km s −1 in the red lobe. The low-resolution spectra are rich in gas 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 L H 2 of 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 H 2 lines (Ṁ out (H 2 ) ∼ 7.5 × 10 −4 M yr −1 ). The comparison between the H 2 and 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 H 2 outflow 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.

Spatially resolved H2emission from a very low-mass star

“…This would lead to a precession period of about four years in order to generate the structures (A, B, and C) at each side of the so-called cavity (opening angle ∼65 • ). This period is too short when compared with typical jet fast precession periods (Rosen & Smith 2004;Caratti o Garatti et al 2008), and not consistent with the longer period suggested by the large-scale jet images (see f08-01 field in Khanzadyan et al 2004).…”

“…However, it is worth noting that these sources are likely to be more massive than ours. This suggests that (1) most of the outflow material is transported by a cooler and denser component than traced by the near-IR H 2 lines, such as the H 2 pure rotational lines (Caratti o Garatti et al 2008); or (2) most of the H 2 has been dissociated, and the jet is mainly atomic. The latter has been observed in other Class I jets, where the measuredṀ H 2 is around one order of magnitude lower than measured from the [Fe ii] emission (Davis et al 2011;Nisini et al 2005).…”

A wide-field near-infrared H22.122μm line survey of the Braid Nebula star formation region in Cygnus OB7

“…In particular, a correlation between outflow luminosity and the bolometric luminosity, L bol , of the driving source may exist. Such a correlation has been demonstrated for low-mass protostars and their outflows (Caratti o Garatti et al 2008); does this relationship extend towards intermediate and high-mass protostars? Unfortunately the current limited dataset for the driving sources in the Braid Nebula region (Table B.1) limits the accuracy of our L bol determinations, although additional observing campaigns are underway to fill the existing gaps in the source SEDs.…”

VLT integral field spectroscopy of embedded protostars: using near-infrared emission lines as tracers of accretion and outflow

“…However, if one plots column densities derived from lines from only the first few vibrational states, a linear fit is usually quite adequate (e.g. Lorenzetti et al 2002;Giannini et al 2004;Davis et al 2004;Gredel 2006;Caratti o Garatti et al 2008;Martín-Hernández et al 2008). By minimising the scatter of points about this line, one can then estimate the extinction.…”