HII Regions and Radio Recombination Lines

Abstract

The hot clouds of ionized gas surrounding bright stars are known as emission nebulae, because their spectra exhibit emission lines. These are often classified further into bright diffuse nebulae, supernova remnants, and planetary nebulae. Diffuse nebulae are associated with the birth of stars whereas supernova remnants and planetary nebulae are associated with the death of stars. Diffuse nebulae have irregular shapes, often filaments, and lie in the plane of galaxies adjacent to the dark molecular clouds from which they formed. Supernova remnants are the remains of exploded stars, a catastrophic process associated with perhaps only about one percent of star deaths. Planetary nebulae are the extended atmospheres of dying, older stars and are found throughout the sphere in which a galaxy originally formed. All emit detectable radio emission.KeywordsElectron TemperatureRadio TelescopeLocal Thermodynamic EquilibriumGalactic CenterGalactic PlaneThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.