Shock Modelling of the Bipolar Outflow Source NGC 6537

Abstract

NGC 6537 is an unusual high excitation bipolar outflow source, with anomalous abundances indicative of a type I nebula. We have recently obtained a range of high resolution spectrophotometry for this source using the 2.5 m Isaac Newton Telescope (Observatorio del Roque de Los Muchachos, La Palma), together with narrow band optical imaging using the 2.6 m Nordic Optical Telescope (Observatorio del Roque de los Muchachos, La Palma). As a consequence, it is apparent that the source optical morphology is suggestive of the presence of an hyperbolic shock outflow surface, similar to those observed in other BPN (e.g. NGC 6302, Hb 5). Line ratio maps also indicate the presence of extremely strong [Nii] emission at the periphery of the outflow, whilst expansion velocities are of order ~ 400 km sec-1. These large shell expansion velocities may in turn be driven by an extremely high velocity wind, which in this case appears to extend over a range ΔV ≥ 3000 km sec-1.