High-resolution spectroscopic observations of the peculiar planetary nebula Me 1-1

Aims:We determined the atmospheric parameters and evolutionary state of the cool stellar component of the peculiar planetary nebula Me 1-1 and analyzed its spatio-kinematic structure.
Methods: High-resolution optical spectroscopy was used in an abundance analysis of the cool component in Me 1-1. Narrow-band images were used to study the nebula.
Results: The stellar parameters derived for the cool star in Me 1-1 are T_eff = 4500 K and log g = 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 = 90 km s^-1. Its estimated mass is 3.5 M_⊙ with a distance of 6 kpc and a luminosity of 370 L_⊙. The cool star in Me 1-1 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 Me 1-1 is an edge-on ring with incipient bipolar lobes. The central star is displaced ~400 AU from the center of the nebula. The expansion velocity of the ring ranges from 10 and 13 km s^-1 in the different emission lines. Broad (≃600 km s^-1) wings are detected in the Hα emission, probably with a stellar origin. A comparison of Me 1-1 with other ring-like planetary nebula shows that most of them host off-center binary central stars.

Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).