2008A&A...477..535P

We determined the atmospheric parameters and evolutionary state of the cool stellar component of the peculiar planetary nebula Me1-1 and analyzed its spatio-kinematic structure. High-resolution optical spectroscopy was used in an abundance analysis of the cool component in Me1-1. Narrow-band images were used to study the nebula. The stellar parameters derived for the cool star in Me1-1 are T_eff=4500K and logg=2.0, which correspond to a spectral type of K(1-2) II. This star is rapidly rotating with a projected rotational velocity of V_rot=90km/s. Its estimated mass is 3.5M_☉ with a distance of 6kpc and a luminosity of 370L_☉. The cool star in Me1-1 has nearly solar iron and calcium abundances. Barium, a monitor of s-process nucleosynthesis, is not enriched. We show that this cool star has reached the base of the RGB and its accreted matter has been diluted by the deepening convective envelope. The images strongly suggest that Me1-1 is an edge-on ring with incipient bipolar lobes. The central star is displaced ∼400AU from the center of the nebula. The expansion velocity of the ring ranges from 10 and 13km/s in the different emission lines. Broad (≃600km/s) wings are detected in the Hα emission, probably with a stellar origin. A comparison of Me1-1 with other ring-like planetary nebula shows that most of them host off-center binary central stars.