Numerical Simulations of HH 555

Abstract

We present three-dimensional (3D) gasdynamic simulations of the HerbigHaro object HH 555. HH 555 is a bipolar jet emerging from the tip of anelephant trunk entering the Pelican Nebula from the adjacent molecularcloud. Both beams of HH 555 are curved away from the center of the H IIregion. This indicates that they are being deflected by a sidewindprobably coming from a star located inside the nebula or by theexpansion of the nebula itself. HH 555 is most likely an irradiated jetemerging from a highly embedded protostar, which has not yet beendetected. In our simulations we vary the incident photon flux, which inone of our models is equal to the flux coming from a star 1 pc awayemitting 5 x 10(48) ionizing (i.e., with energies above the H Lymanlimit) photons per second. An external, plane-parallel flow ( a``sidewind'') is coming from the same direction as the photoionizingflux. We have made four simulations, decreasing the photon flux by afactor of 10 in each simulation. We discuss the properties of the flow,and we compute H alpha emission maps ( integrated along lines of sight).We show that the level of the incident photon flux has an importantinfluence on the shape and visibility of the jet. If the flux is veryhigh, it causes a strong evaporation of the neutral clump, producing aphotoevaporated wind traveling in the direction opposite to the incidentflow. The interaction of the two flows creates a double shock ``workingsurface'' around the clump, protecting it and the jet from the externalflow. The jet only starts to curve when it penetrates through theworking surface.