Kinematics and H$_{\sf 2}$ morphology of the multipolar post-AGB starIRAS 16594-4656

• Published in: Astronomy and astrophysics (Berlin) 2008-03, Vol.480 (3), p.775-783
• Main Authors: Van de Steene, G.C., Ueta, T., van Hoof, P. A. M., Reyniers, M., Ginsburg, A. G.
• Format: Article
• Language: English
• Subjects: ISM: molecules; outflows; shock waves; stars: AGB and post-AGB; stars: individual : IRAS 16594-4656; stars: winds
• ISSN: 0004-6361; 1432-0746
• DOI: 10.1051/0004-6361:20078880

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]. Aims.The goal is to determine the location of the H2 and [Fe ii] shock emission, to determine the shock velocities, and to 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-1 and the presence of a neutral, very high-density region with ne about $3\,\times\,10^6$ to $5\,\times\,10^7$ cm-3. However, the [Fe ii] emission is single-peaked. It has a Gaussian FWHM of 30 km s-1 and a total width of 62 km s-1 at 1% of the peak. The Paβ profile is even wider with a Gaussian FWHM of 48 km s-1 and a total width of 75 km s-1 at 1% of the peak. Conclusions.The H2 emission is excited in a slow 5 to 20 km s-1 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.