Rummaging inside the Eskimo's parka: variable asymmetric planetary nebula fast wind and a binary nucleus?

Abstract

We report on high-resolution optical time series spectroscopy of the central star of the `Eskimo' planetary nebula NGC 2392. Data sets were secured with the European Southern Observatory (ESO) 2.3 m in 2006 March and Canada-France-Hawaii Telescope (CFHT) 3.6 m in 2010 March to diagnose the fast wind and photospheric properties of the central star. The He I and He II recombination lines reveal evidence for clumping and temporal structures in the fast wind that are erratically variable on time-scales down to ∼30 min (i.e. comparable to the characteristic wind flow time). We highlight changes in the overall morphology of the wind lines that cannot plausibly be explained by line-synthesis model predictions with a spherically homogeneous wind. Additionally, we present evidence that the ultravoilet line profile morphologies support the notion of a high-speed, high-ionization polar wind in NGC 2392. Analyses of deep-seated, near-photospheric absorption lines reveals evidence for low-amplitude radial velocity shifts. Fourier analysis points tentatively to an ∼0.12-d modulation in the radial velocities, independently evident in the ESO and CFHT data. We conclude that the overall spectroscopic properties support the notion of a (high-inclination) binary nucleus in NGC 2392 and an asymmetric fast wind.