van de Steene, G. C. ; Ueta, T. ; van Hoof, P. A. M. ; Reyniers, M. ; Ginsburg, A. G.

published in Astronomy and Astrophysics, 480, pp. 775-783 (2008)

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]. 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 Paß 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 × 106 to 5 × 107 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 Paß 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 Paß emission also appears to originate close to the star. Based on observations collected at the Gemini-South with the Phoenix instrument under GS-2003A-Q-41, and VLT under 65.L-0615(A).

DOI: 10.1051/0004-6361:20078880
Links: link