symbiotic stars

A term coined in 1928 by P. Merrill for stars with a particular type of unusual combination spectrum. Features of both a cool star and emission lines characteristic of a very-high-temperature gas are present. The normal interpretation is that the cool star is losing mass to a dwarf or white dwarf companion. Energy from a hot spot or heated accretion disc could ionize a large volume of the infalling gas to account for the nebular-type emission lines. Such stars are also variable because of the irregularity of the mass transfer and eclipse of emitting material by the large cool star. They are also known as Z Andromedae stars.