Shock excitation of the knots of Hen 3-1475

Abstract

We present new optical STIS HST spectroscopic observations of the jets of the proto-planetary nebula Hen 3-1475. The excitation conditions of the knots of Hen 3-1475 are derived from the observed optical spectra, confirming that the knots are shock excited. The shocked spectra are qualitatively reproduced by simple “3/2”D bow shock models. We present a set of bow shock models devoted to planetary nebulae, and discuss the effects of the pre-ionization conditions, the bow shock velocity, the bow shock shape and the chemical abundances on the predicted spectra. To explore the reliability of the “3/2”D bow shock models, we also compare the observed spectra of other three proto-planetary nebulae (M 1–92, M 2–56 and CRL 618) to the predicted spectra.