M1-46: A case study on multiple-shell planetary nebula formation

We discuss in detail the evolutionary path of the multiple-shell planetary nebula M1-46, in the light of our new observations. The velocities of the halo and main nebula correspond to a dynamical time lap between the shells of about 6.8 x 10(4) yr. By means of a non-LTE analysis of the central star's spectrum, we derived a stellar temperature of T-eff = 45,000 K, which, coupled to the visual magnitude and an appropriate bolometric correction, gives a stellar luminosity of 5370 L(circle dot). The mass of the central star has been evaluated to be 0.6 M(circle dot), and its interpulse time on the asymptotic giant branch is 7.6 x 10(4) yr. The agreement between the observed intershell time lap and the evolutionary interpulse time lap points to the fact that the formation of this planetary nebula could be ascribed to the gasping mass loss associated with the thermal pulses at the thermally pulsating asymptotic giant branch. The high-resolution spatially resolved observations reveal the presence of different kinematical components in the main nebula which cannot be understood in a homogeneous expanding shell. scenario. As regards the chemical abundances, M1-46 has the typical abundances of a type II planetary nebula. No definite abundance gradient between the shells is found.