Observational 2D model of H₂ emission from a bow shock in the Orion Molecular Cloud^*

¹ Observatoire de Paris & Université de Cergy-Pontoise, LERMA, UMR 8112 du CNRS, 92195 Meudon Cedex, France e-mail: lars.kristensen@u-cergy.fr
² Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark
³ Institut d'Astrophysique Spatiale, UMR 8617 du CNRS, Université de Paris Sud, 91405 Orsay, France
⁴ Max Planck Institut für Astronomie, 69117 Heidelberg, Germany

Received: 15 June 2007
Accepted: 24 October 2007

Abstract

Aims.We present a new method for reproducing high spatial resolution observations of bow shocks by using 1D plane parallel shock models. As an example we analyse one bow shock located in the Orion Molecular Cloud (OMC1).

Methods.We use high spatial resolution near-infrared observations of H₂ rovibrational emission to constrain shock models. These observations have been made at the ESO-VLT using a combination of the NACO adaptive optics system and infrared camera array and the Fabry-Perot interferometer. Three rovibrational H₂ lines have been observed: 1-0 S(1) at 2.12 μm, 1-0 S(0) at 2.23 μm and 2-1 S(1) at 2.25 μm. The spatial resolution is 015 ~ 70 AU. We analyse a single bow shock located in our field, featuring a very well defined morphology and high brightness.

Results.One dimensional shock models are combined to estimate the physical properties of pre-shock density, shock velocity and transverse magnetic field strength along the bow shock. We find that the pre-shock density is constant at ~5  10⁵ cm^-3 and shock velocities lie between ~35 km s^-1 in the wings of the shock and ~50 km s^-1 at the apex. We also find that the transverse magnetic field is stronger at the apex and weaker further down the wings varying between ~2 and 4 mGauss. Predictions of shock velocity and magnetic field strength agree with previous independent observations.