The Dark Secrets of Gaseous Nebulae: Highlights from Deep Spectroscopy
The existence and distribution of the chemical elements and their isotopes are a consequence of nuclear processes that have taken place in the past during the Big Bang and subsequently in stars and in the interstellar medium (ISM) where they are still ongoing (Pagel, 1997). A large body of our knowledge of the distribution and production of elements in the Universe rests on observations and analyses of photoionized gaseous nebulae. Ionized and heated by strong ultraviolet (UV) radiation œelds, photoionized gaseous nebulae glow by emitting strong emission lines (Osterbrock and Ferland, 2005). They are therefore also commonly named emission-line nebulae.