This object, also known as Sh2-313, is a Stromgren sphere located 1200 light years away in the southern constellation of Hydra at a declination of -23 degrees. The low declination makes it hard for me to image this object clearly. The apparent size of the image is slightly larger than our full moon, at just over half a degree.
For most of its known existence, this object has been classified as an old planetary nebula. But looking carefully at the image, and comparing to
many other planetary nebulae structures, it is clear that the structure of this object is different from a planetary nebula in many ways. The star at the center is very bright, and appears to be at least a double star. The structure is not circular in nature and has many arcing and straight line features which are typcially not seen in a PN. Finally, there is no symmetry apparent in the structure. Recent scientific work has concluded that this object is not a planetary nebula but is a Stromgren sphere. A Stromgren sphere is a region of ionized hydrogen (HII) surrounding a hot, young O-B star.
Interestingly, the bright star at the center of the image is not hot enough to ionize the nebula. Scientists have verified that there is an unseen, hot companion star that powers the nebula. My image shows the bright star to be a binary star, but I don't know if the smaller star is actually the "unseen" star powering the nebula.
My favorite part of the image is the bow shock OIII wave at the center of the image. The other horizontal ridge-type structures also seem to indicated some type of high speed disturbance. It seems that some of these impacts are due to the source star and some may be due to the movement of the nebula through the ISM.
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