Abstract

Based on high-resolution UVES @ VLT spectroscopy and 20 years of HST imaging, we study the internal interactions of Orion Nebula gas with photoionized Herbig-Haro (HH) objects. Our works reveal that the multiple internal gas interactions that take place within the Orion Nebula have an important role in the density structure of the nebula, changing dramatically the local ionization state of the gas. These interactions must be present in an unknown proportion in more distant Galactic and extragalactic star forming regions, where the existence of young stellar objects ensures the presence of protostellar jets such as the HHs. The consideration of this more realistic image of the star forming regions, different from assuming that they are homogeneous environments, can change the assumptions we make on their physical conditions to derive their chemical composition. We will focus on HH529II, HH529III, HH204 and HH514. These objects are located at different distances from the main ionization source of the Orion Nebula, with different ionization / physical conditions and flow velocities. In all HH objects, we find direct evidence of dust destruction, that increases the gaseous abundances of Fe, Ni and Cr, which magnitude seems to be correlated with the flow velocity. By combining the emission of the HH objects and the Orion Nebula we simulate low-resolution spectra with high-density inclusions, finding that some of the classical diagnostics --such as [SII] I(6716)/I(6731)-- underestimate the true density, overestimating the temperature, which can result in erroneous chemical abundance determinations.