Saturday, April 2, 2022

Nebula NGC 3199

NGC 3199 (also known as Gum 28, RCW 48, and BRAN 300A) is an emission nebula and an H II region, located at a distance of around 11,700 light years in the constellation of Carina. It was discovered on the 1st of May 1826 by James Dunlop.

The nebula is around 75 light years across and it’s divided into two components. The first is a bright arc-shaped component, while the second is a dim, diffused, filamentary component. Both of them create a nearly circular nebula. Furthermore, due to the morphology of the bright component, NGC 3199 has been nicknamed the Banana Nebula. 

The nebula is powered by a supermassive, hot star known as WR 18 (HD 89358). This is a WN4 Wolf-Rayet (WR) star with a surface temperature of 112,000 Kelvin. The immense radiation pressure and the super strong wind of the star are responsible for the creation of a bright bow-shock in its immediate environment (i.e., in this case the bright arc-shaped structure).

WR stars are a rare class of very massive and very hot stars that display spectra with broad emission lines of ionised helium, nitrogen and carbon. They have super strong stellar winds, thus they have a very high mass loss rate. Based on observations the mass loss rate of WR 18 has been estimated at 0.000027 solar mass/yr. For reference the mass loss rate of a sun-like star is 1-10 billion times smaller.

In an environment like the one of NGC 3199, a WR star is not only responsible for its ionisation, but due its immense UV emission and strong stellar wind, compress the nearby interstellar medium, thus triggering star formation.

Image: Composite optical image of NGC 3199 taken with a small telescope. The image was created by using broadband filters (RGB), together with narrow band filters that are focused on the emission of ionised oxygen ([O III]), ionised hydrogen (Hα), and ionised sulphur ([S II]). 

Image Credit:  Adam Block/Mike Selby

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