HH-110 - THE GRAZING COLLISION OF A HERBIG-HARO FLOW WITH A MOLECULARCLOUD CORE

The HH 110 jet is a major collimated Herbig-Haro flow in Orion. Despit e careful searches at optical, infrared and sub-mm wavelengths, attemp ts to find the driving source along its well defined flow axis have fa iled. We present deep large-field interference-filter CCD images which reveal the presence of another fainter HH flow, here labelled HH 270, to the north-east of HH 110. This flow is driven by an embedded near- infrared source, which is possibly identical to the 5 L(.) embedded cl ass I source IRAS 05489+0256. We propose that the source driving HH 27 0 is also responsible for HH 110, and that the HH 270 flow suffers a g razing collision with the dense molecular cloud core from which HH 110 is seen to emerge. This collision deflects and shocks the flow so tha t it re-appears as HH 110. This scenario is supported by geometric and kinematic evidence: firstly, the HH 270 flow axis points towards the beginning of HH 110; secondly, proper motion measurements of the brigh test knot in HH 270, knot A, reveal a large tangential motion of 300 k m/sec directly towards HH 110 knot A, the apex of this flow; thirdly, HH 110 knot A has a two-component structure consisting of a head and a neck, the former moving in the direction defined by the HH 270 flow, and the latter in the direction of the HH 110 flow, suggesting that we here see directly the point of impact and deflection. Moreover, there is evidence for weak shocks approximately parallel with the HH 110 ho w which appear to be due to separate collisions with obstructions in t he flow. We assume that the HH 270/110 flow is not far from the plane of the sky, an assumption supported by the high proper motion of HH 27 0 A and the low radial velocity of HH 110. The observed angle between HH 270 and HH 110 (58 degrees), is then close to the true deflection a ngle which results from the flow collision. Using the observed velocit ies and the analytical models of Cant6 et al. (1988), we find theoreti cally that the deflection angle should be about 62 degrees. The simila rity of these values supports the idea that HH 110 is the result of a grazing collision of the HH 270 flow with a cloud core.