Abstract.Observations are reported of IR emission of H2 from a region of the Orion molecular cloud (OMC1) between the Becklin-Neugebauer object and IRc2 to the north and the Trapezium stars to the south. Data were obtained using the ESO 3.6 m telescope in the K-band around 2 µm with the ADONIS adaptive optics system. Images of H2 v = 1−0 S(1) show a spatial resolution of ∼0.15 . Detailed investigations of the distribution of sizes of structures in our images have been performed by area-perimeter analysis, Fourier analysis and brightness distribution studies. These demonstrate that structure is not fractal but shows a preferred scales of between 3 10 −3 and 4 10 −3 pc. In an attempt to estimate the density in observed structures, predictions of both shock models and photodissociation region models have been compared with measured emission brightness in the H2 v = 1−0 S(1) line. Magnetic (C-type) shocks with velocities of 30 km s −1 and pre-shock densities of 10 6 cm −3 yield the best representation of our data, notwithstanding significant discrepancies for the brightness ratio between v = 2−1 S(1) and v = 1−0 S(1) lines. Our results show that post-shock densities are several times 10 7 cm −3 . This is sufficiently high that the passage of C-type shocks in Orion yields gravitational instability which may in turn trigger star formation in the post-shock gas.

Abstract.Observations are reported of IR emission in H 2 , around 2 µm in the K-band, obtained with the ESO 3.6 m telescope using the ADONIS adaptive optics system. Data cover a region of the Orion Molecular Cloud north of the Trapezium stars and SW of the Becklin-Neugebauer object. Excellent seeing yielded diffraction limited images in the v = 2−1 S(1) line at 2.247 µm. Excitation temperature images were created by combining these data with similar data for H 2 emission in the v = 1−0 S(1) line reported earlier ). Shock models are used to estimate densities in emitting clumps of material. In local zones with high excitation temperatures, post-shock densities are found to be as high as several times 10 8 cm −3 , an order of magnitude denser than our previous estimates. We propose that the nature of these zones is dictated by the combined activity of shocks, which create dense structures, and the powerful radiation field of θ 1 C Ori which photoevaporates the boundaries of these structures.

No abstract