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context: The spectrum of IRAS 16594-4656 shows shock excited H_2 emission andcollisionally excited emission lines such as[O I],[C I],and [Fe II]. aim: Thegoal is to determine the location of the H_2 and [Fe II] shock emission, todetermine the shock velocities,and constrain the physical properties in theshock. methods: High resolution spectra of the H_2 1-0 S(1),H_2 2-1 S(1), [FeII], and Pa$\beta$ emission lines were obtained with the near infraredspectrograph Phoenix on Gemini South. results: The position-velocity diagramsof H_2 1-0 S(1), H_2 2-1 S(1), and [Fe II] are presented. The H_2 and [Fe II]emission is spatially extended. The collisionally excited [O I] and [C I]optical emission lines have a similar double peaked profile compared to theextracted H_2 profile and appear to be produced in the same shock. They allindicate an expansion velocity of ~8 km/s and the presence of a neutral, veryhigh density region with $n_{\rm e}$ about 3 x 10^6 to 5 x10^7 cm$^{-3}$. The[Fe II] emission however is single peaked. It has a gaussian FWHM of 30 km/sand a total width of 62 km/s at 1% of the peak. The Pa$\beta$ profile is evenwider with a gaussian FWHM of 48 km/s and a total width of 75 km/s at 1% of thepeak. conclusions: The H$_2$ emission is excited in a slow 5 to 20 km/s shockinto dense material at the edge of the lobes, caused by the interaction of theAGB ejecta and the post-AGB wind. The 3D representation of the H_2 data shows ahollow structure with less H_2 emission in the equatorial region. The [Fe II]emission is not present in the lobes, but originates close to the central starin fast shocks in the post-AGB wind or in a disk. The Pa$\beta$ emission alsoappears to originate close to the star.

Kinematics and H_2 morphology of the multipolar Post-AGB star IRAS 16594-4656