Molecular hydrogen in S106

Abstract

Emission from the |$\upsilon=1-0\enspace S(1)$| line of molecular hydrogen at 2.122 μm has been found and mapped in the bipolar nebula S106. The emission is extended along an axis running approximately N–S, similar to the radio and mid-infrared emission. More emission is seen from the north lobe than the south, and generally there is an anti-correlation between the H2 and radio emission. In particular, the strongest H2 emission comes from a peak at the outer boundary of the northern radio lobe. The total luminosity in H2 emission can be accounted for completely either by shock excitation driven by mass loss at a rate close to that calculated by other methods, or by ultraviolet excitation by photons from an O9.0 ZAMS star. Emission line ratios in the 2.0–2.5 μm region are indeed consistent with a combination of shock- and ultraviolet-excitation mechanisms.