planetary nebula

A planetary nebula (PN or PNe) is ionized gas around an asymptotic giant branch star. The term stems from the era of their first observation since given the observation methods of the time, they resembled planets.

Such nebula are theorized to be matter ejected by pulses in the helium burning of an AGB star (thermal pulse or helium runaway shell).

They are presumed to live on the order of ten thousand years.

Vorontsov-Velyaminov planetary nebula types:

• Type I - stellar image.
• Type II - smooth disk.
• Type III - irregular disk.
• Type IV - ring structure.
• Type V - irregular form.
• Type VI - anomalous form.