Bow-Tie Nebula (NGC 40)
The planetary nebula NGC 40 was discovered on 25 November 1788 by Wilhelm Herschel with its 18.7 inch reflector.  The nature of a planetary nebula was discovered by the American astronomer Williamina Fleming. Because of its appearance, the nebula was nicknamed «Bow-Tie Nebula».
Planetary nebulae are the result of a sun-like star that ejected material into space during its transformation from a red giant to a white dwarf. The central star of NGC 40 is a recently formed proto-white dwarf with a surface temperature of about 50'000 K. The nebula is about 3000-4000 light years away and based on its angular extent of about 1.2 x 0.75 arc minutes, it measures about 1.2 light years in diameter. The outermost regions of earlier eruptions extend roughly four to five times into space.
Most of the radiation from the nebula comes from gas clouds, which are heated to around 10'000 K by the light of the star. This is shown in red in Fig. 2. Some regions have also been heated to several million degrees Celsius and radiate in the X-ray range (blue areas). Here, with a stellar wind at a speed of 894 km/s, ejected gas from the star collides with interstellar material and exerts high compression forces. In about 30'000 to 40'000 years, the radiation and the stellar wind of the white dwarf will fade and the glowing nebula will dissolve. [196, 296]
|Designations||PN G120.0+09.8: NGC 40, PK 120+09.1, ARO 1, VV 1, VV' 3|
|Right Ascension (J2000.0)||00h 13m 01s|
|Declination (J2000.0)||+72° 31' 20"|
|Radial Velocity||-20.4 km/s ± 0.9 km/s|
|Expansion Velocity||29.0 km/s (O-III), 26. km/s (N-II)|
|C-Star Designations||AG82 2, CSI+72-00102 0, DC 22918, Em* CDS 11, HD 826, PLX 31|
|C-Star Magnitude||11.14 mag (U filter), 11.82 mag (B filter), 11.58 mag (V filter)|
|C-Star Spectral Type||WC 8|
The planetary nebula NGC 40 is located in the constellation Cepheus. It is circumpolar and is highest in the night sky from May to December.