Kinematics and H2 morphology of the multipolar Post-AGB star IRAS 16594-4656
Abstract
context: The spectrum of IRAS 16594-4656 shows shock excited H2 emission and collisionally excited emission lines such as[O I],[C I],and [Fe II]. aim: The goal is to determine the location of the H2 and [Fe II] shock emission, to determine the shock velocities,and constrain the physical properties in the shock. methods: High resolution spectra of the H2 1-0 S(1),H2 2-1 S(1), [Fe II], and Paβ emission lines were obtained with the near infrared spectrograph Phoenix on Gemini South. results: The position-velocity diagrams of H2 1-0 S(1), H2 2-1 S(1), and [Fe II] are presented. The H2 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 the extracted H2 profile and appear to be produced in the same shock. They all indicate an expansion velocity of ~8 km/s and the presence of a neutral, very high density region with n e about 3 x 106 to 5 x107 cm-3. The [Fe II] emission however is single peaked. It has a gaussian FWHM of 30 km/s and a total width of 62 km/s at 1% of the peak. The Paβ profile is even wider with a gaussian FWHM of 48 km/s and a total width of 75 km/s at 1% of the peak. conclusions: The H2 emission is excited in a slow 5 to 20 km/s shock into dense material at the edge of the lobes, caused by the interaction of the AGB ejecta and the post-AGB wind. The 3D representation of the H2 data shows a hollow structure with less H2 emission in the equatorial region. The [Fe II] emission is not present in the lobes, but originates close to the central star in fast shocks in the post-AGB wind or in a disk. The Paβ emission also appears to originate close to the star.