Kinematics and H morphology of the multipolar post-AGB star IRAS 16594-4656*
Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium e-mail: [gsteene;firstname.lastname@example.org]
2 Department of Physics and Astronomy, University of Denver, 2112 E. Wesley, Denver, CO 80208, USA e-mail: email@example.com
3 Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium e-mail: firstname.lastname@example.org
4 Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309, USA
Accepted: 21 December 2007
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 to 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.
Key words: shock waves / stars: AGB and post-AGB / stars: winds, outflows / stars: individual : IRAS 16594-4656 / ISM: molecules
© ESO, 2008