- Ville Puoskari
Ancient planetary nebula HDW2
This planetary nebula was first discovered by an American astronomer Stewart Sharpless in 1959. He included it in his catalogue of HII regions with an identification Sh2-200. Later in 1983 it was included in the HDW catalogue of possible planetary nebulae by the astronomers Herbert Hartl, Johann Dengel and Ronald Weinberger. In 2017 spectra of this object was taken by other professional astronomers and this verified their observations, confirming that this was indeed a planetary nebula. These kinds of nebulas form at the end of the life of a star that is around 1-8 solar masses. Larger stars than this will explode as a supernova. Planetary nebulas last only few tens of thousands of years as their shell expands further away from the central star, eventually fading away to space. Sh2-200 is located in the constellation of Cassiopeia, which is near zenith at this time of the year in Finland. This made it possible to get good data for a long time because this object is very faint and any haze in the atmosphere would definedly be a problem. It seems to respond best to H-alpha filter, revealing some ionized hydrogen on the left side of the image that maybe related to the planetary nebula. However I couldn't verify this from any reliable source. There is some details in the core that seem to respond best to Ha filter - but mostly I would recommend using an OIII filter instead to reveal more subtle details in the nebulosity.