HH135/HH136 – a luminous H₂ outflow towards a high-mass protostar

Max-Planck Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: gredel@mpia.de

Received: 21 December 2005
Accepted: 4 May 2006

Abstract

Context.Molecular hydrogen observations towards Herbig-Haro objects provide the possibility of studying physical processes related to star formation.

Aims.Observations towards the luminous IRAS source IRAS 11101-5928 and the associated Herbig-Haro objects HH135/HH136 are obtained to understand whether high-mass stars form via the same physical processes as their low-mass counterparts.

Methods.Near-infrared imaging and spectroscopy are used to infer H₂ excitation characteristics. A theoretical H₂ spectrum is constructed from a thermal ro-vibrational population distribution and compared to the observations.

Results.The observations reveal the presence of a well-collimated, parsec-sized H₂ outflow with a total H₂ luminosity of about . The bulk of the molecular gas is characterized by a ro-vibrational excitation temperature of  K. A small fraction (0.3%) of the molecular gas is very hot, with excitation temperatures around 5500 K. The molecular emission is associated with strong [FeII] emission. The H₂ and [FeII] emission characteristics indicate the presence of fast, dissociative J-shocks at speeds of  km s^-1. Electron densities of –4000 cm^-3 are inferred from the [FeII] line ratios.

Conclusions.The large H₂ luminosity combined with the very large source luminosity suggests that the high-mass protostar that powers the HH135/HH136 flow forms via accretion, but with a significantly increased accretion rate compared to that of low-mass protostars.