Tuesday, Jan 7, 2025

HFG1 was discovered in the Milky Way Emission Line Study in 1982 by Heckathorn, Fesen and Gull. It is defined as a type F planetary nebula by Tweedy and Kitter, meaning that is appears to be uniformly filled. HFG1 (lower left) was created by the central star V664 Cas. This is not a single star, but a dense binary star system consisting of a white dwarf and a sun-like star, which are only a few million kilometres apart and orbit every 14 hours. Because the binary system V664 Cas moves very fast (at 29 to 59 kilometres per second) and ploughs through the interstellar medium together with the nebula, a bluish arc shock occurs. Abell 6 is at image centre. This nebula also is emitting light in the OIII band while it's intensity in the range of hydrogen is low. Abell 6 appears to be circular with a diameter of almost 3 arc minutes. It's edge is partly brightened & terminates sharply. The central star is very faint and can just barely be seen.