Molecular jets driven by high-mass protostars: a detailed study of the IRAS 20126+4104 jet*
Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany e-mail: [caratti;jochen]@tls-tautenburg.de
2 Centre for Astrophysics and Planetary Science, University of Kent, Canterbury, CT2 7NH, UK e-mail: email@example.com
3 INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio, Italy e-mail: [giannini;nisini]@oa-roma.inaf.it
Accepted: 13 March 2008
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 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 H2 gas along the flow.
Methods. The jet was investigated by means of near-IR H2 and  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 H2 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 H2 emission, and relatively faint  (NIR),  and  (FIR) emission is observed in the region close to the source. A warm H2 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 of the jet is , 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 H2 lines ((H yr-1). The comparison between the H2 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 H2 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.
Key words: stars: pre-main-sequence / infrared: ISM / ISM: jets and outflows / ISM: kinematics and dynamics / individual objects: IRAS 20126+4104
© ESO, 2008