Highly Collimated Molecular Hydrogen Jets near IRAS 05487+0255: Near-Infrared Imaging and Spectroscopy

We present new narrowband near-infrared images together with K-band spectra of highly collimated bipolar jets close to the IRAS 05487+0255 source. The jets are located ~50'' west of the Herbig-Haro 110 outflow. The jets are not visible at optical wavelengths and therefore do not fall into the "standard" Herbig-Haro object classification scheme. Nevertheless, they belong to an ever growing group of molecular hydrogen jets associated with young stellar objects that are optically undetected. The jets are very well collimated, with length-to-width ratios of ~10-20. The spectra of the jet and its counterjet in the K band show a limited number of H₂ emission lines that make it difficult to obtain an accurate excitation temperature. We estimate T_ex = 1104±67 K and T_ex = 920±156 K for the red and blue jet components, respectively. The radial velocities of the jet and counterjet, based on the shift of the (1,0) S(1) 2.121 μm line, are ~-275 ± 50 km s^-1 and ~180 ± 50 km s^-1, respectively, suggesting an angle of ~30°-45° between the jet and the line of sight. The H₂ emission of the entire jet extends for at least 40'', ~0.1 pc at the distance of Orion. If the flow velocity is comparable to that of the radial velocities, then the dynamical age of the system is quite short (~500 yr), consistent with a young jet arising from an embedded source. Entrainment in a turbulent mixing layer may explain this morphology and spectral character.