2014A&A...561A..81B

The shaping process of planetary nebulae (PNe) takes place during the short transition from the asymptotic giant branch (AGB) phase to the white dwarf stage. The young PN K3-35 represents a unique case where a small-sized water maser ring has been linked to the launch of collimated outflows that shape the nebula. The contrasting optical and radio continuum morphologies of K3-35 indicate that they disclose different structural components that are apparently unconnected. To bridge the gap between optical and radio continuum observations, we present here new broadband and narrowband near- and mid-IR images of K3-35. These images, and their comparison with optical and radio continuum images, are revealing. The radio continuum and mid-IR images are dominated by a compact source at the core of K3-35 whose emission gives evidence of very dense ionized material embedded within a dust cocoon. The emission from the core, obscured at optical wavelengths, is faintly detected in the K_s band. We suggest that the dust may shield the water molecules at the inner ring from the central star ionizing radiation. The precessing collimated outflows, very prominent in radio continuum, are also detected in mid-IR, very particularly in the [S iv] image. The mid-IR emission from these outflows consist mostly of ionized material, although the broadband filter at 11.85 µm seems to imply that a small amount of dust may be carried out by the outflow. The interactions of these outflows with the nebular shell result in shocks that excite the emission of H₂ as well as low-excitation lines from ionized species, such as [N ii] at the tips of the outflows.