Planetary Nebulae (5 objects)
Go gently into that good night. When a sun-like star's nuclear fuel is exhausted, the core starts to shrink. The gravitational energy thus released heats both the core and the atmosphere even faster than the previously sedate nuclear furnace. The atmosphere is expelled, leaving a naked very hot tiny core (white dwarf). The intense UV from the hot core causes the atmosphere to glow in H-alpha (especially in an outer shell) and O-III (especially near in). Binary companions, strong magnetic fields, and equatorial dust lanes conspire to produce beautiful and convoluted shapes, seen very differently according to our viewing angle.
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NGC 246 is a moderately large (4 min arc) moderately bright (mag 8.2) planetary nebula in Cetus, which has a famously skull-like, or at least "scary face" look to it.
Here, we've managed to resolve the mag 12 white dwarf separately from its brighter binary companion. The ESO docco for this object describes it as moving upward relative to the interstellar medium, resulting in a noticeably brighter shock front at the upper leading edge.
H-alpha (yellow) 8 hrs, OIII (blue) 8 hrs, both in 1 hr unbinned subs. There was negligible SII and we've not included any here.
