NGC 2392. A curious planetary nebula

 

 

NGC 2392 (it is also known as the Eskimo Nebula or Clown face Nebula, although these names were discontinued by the IAU in 2020 because of the potential perception as offensive) is a small (48×48 arcsec) planetary nebula (PN) located at a distance of about 6500 ly in the constellation Gemini. Besides its small size, it presents an intricate structure that is due to its origin as a stellar mass ejection of a very hot central star system.

The central star of the planetary nebula NGC 2392 is a hot, evolved, hydrogen-deficient star classified as a [WC] type Wolf-Rayet central star, or more precisely, a [WR] central star of a planetary nebula. It has been classified as a [WC3] or [WR] type star, which means it shows strong emission lines of highly ionized carbon (C IV) and helium (He II), typical of Wolf-Rayet stars. Its surface temperature is very high — estimates place it at around 40,000 to 75,000 K. It is also described by some earlier authors as a spectral type O(H)6f.

This central star has an also hot companion, most probably a white dwarf with a calculated mass of about 0.6 solar masses. The constant mass ejection from the WR star, together with this companion’s mass, may be the explanation for the also easily detected X-ray emission.

Like many other PNe, NGC 2392 has a jet emitted in opposite directions. This jet was discovered in 1985 by Gieseking et al.  but due to its extreme faintness it was not imaged until 2021 by Guerrero et al. using the Gran Telescopio de Canarias (GTC, 10.4 m) and NII filters (see image below, superimposed to a Hubble image). The red and blue color code means approaching (blue) or receding (red) jet branch.

 

An attempt to also show this feature in this image was done by taking several images of this object through an NII filter, but no trace of the jet was found. The exposure times used for this image, due to its high dynamic range) were from 40 seconds up to 40 minutes.