Near-infrared echelle spectroscopy of protoplanetary nebulae: Probing the fast wind in H2

Echelle spectroscopy of H 2 2.122 ?m, [Fe II] 1.644 ?m and Br? line emission from a very young planetary nebula (PN), IRAS 21282+5050, and from four protoplanetary nebulae (PPN), IRAS 19343+2926 (M 1-92), IRAS 17150-3224 (AFGL 6815), IRAS 17423-1755 (Hen 3-1475) and IRAS 17441-2411, is presented. H 2 line emission is detected in discrete shock fronts in the lobes of each nebula, regardless of source spectral type [although non-detections in IRAS 09371 + 1212 (Frosty Leo) support claims that late spectral types do not produce bright H 2 line emission]. In IRAS 17150-3224, we also uncover possible signs of rotation, as would be expected if the H 2 features were excited in a magnetocentrifugal disc wind. [Fe II] 1.644 ?m emission was detected in only one source, M 1-92 (notably, the source with the brightest H 2 features). Again, the emission is predominantly excited in high-velocity shocks in the bipolar lobes of the PPN. The H 2 and [Fe II] observations of M 1-92, and the complex H 2 profiles in IRAS 21282+5050, are explained using the shock models of Smith and collaborators. We show that bow shock models are generally able to account for the observed line profiles, peak velocities, the double-peaked profiles in IRAS 21282+5050, and the spatial distribution of H 2 and [Fe II] in M 1-92. J-type bow models are adequate in each case, i.e. a strongly magnetized wind is not required. Finally, Br? is detected in each of the five targets; in absorption in the G-type PPN, though in emission in the O- and B-type sources. Br? emission is detected predominantly towards the near-infrared (near-IR) continuum peak in each PPN, with only very weak emission detected in the extended lobes of the O- and B-type sources. In Br?, low peak velocities, though very broad profile widths, are measured in each target, regardless of the nebula inclination angle. The emission must therefore derive from ionized regions in a fast wind very close to the central star (rather than from shocks in the bipolar lobes), or, in the late-type sources, from absorption in an equatorial torus.