All SX Phoenicis variable
All SX Phoenicis variables belong to a class of stars described by this adjective, and S Doradus is the prototype of another class of stars described by this adjective. In the spectra of active galactic nuclei, a feature described with this adjective and "big" is caused by thermal emission from an accretion disk. A cloud named for this adjective appears in a galaxy-color magnitude diagram and is mostly populated by spirals. Eta carinae and P cygni are examples of a type of (*) "luminous variable" described by this adjective, which also describes the supergiant Rigel. Along with ultraviolet and visible, this color is found in the name of the most common photometric system. Class O stars appear this color, as do a class of stars that lie to the left of the turnoff point of the main sequence. For 10 points, name this color of a class of "stragglers" and the planet Neptune.
All SX Phoenicis variables belong to a class of stars described by this adjective, and S Doradus is the prototype of another class of stars described by this adjective.
blue