Tomography of the unique on-going jet in the planetary nebula NGC 2392

Abstract

Jets (fast collimated outflows) are claimed to be the main shaping agent of the most asymmetric planetary nebula (PNe) as they impinge on the circumstellar material at late stages of the asymptotic giant branch (AGB) phase. The first jet detected in a PN was that of NGC 2392, yet there is no available image because its low surface brightness contrast with the bright nebular emission. Here we take advantage from the tomographic capabilities of GTC MEGARA high-dispersion integral field spectroscopic observations of the jet in NGC 2392 to gain unprecedented details of its morphology and kinematics. The jet of NGC 2392 is found to emanate from the central star, break through the walls of the inner shell of this iconic PN and extend outside the nebula's outermost regions with an Sshaped morphology suggestive of precession. At odds with the fossil jets found in mature PNe, the jet in NGC 2392 is currently being collimated and launched. The high nebular excitation of NGC 2392, which implies a He ++ /He ionization fraction too high to be attributed to the known effective temperature of the star, has been proposed in the past to hint at the presence of a hot white dwarf companion. In conjunction with the hard X-ray emission from the central star, the present-day jet collimation would support the presence of such a double-degenerate system where one component undergoes accretion from a remnant circumbinary disk of the common envelope phase.

Planetary Nebulae: Sources of Enlightenment

“…28), was found by Jones et al (2014) to contain a post-CE double-degenerate nucleus with a period of ∼1.2 days, strengthening the association of these outflows with binary evolution. Additional evidence is provided by Guerrero et al (2021), who have for the first time directly imaged the jets in NGC 2392, S-shaped like those in Fg 1, and which they deduce are being actively launched now, rather than representing remnants of earlier ejections. Also, based on the observed hard x-ray stellar emission and high level of nebular excitation, they conclude that the companion to NGC 2392's central star is a white dwarf, adding to the short list of double-degenerate systems in PNe.…”