root@utastro.UUCP (charles) (03/01/85)
A star called Epsilon Aurigae gets dimmer every 27 years. More on why -- after this. March 1 Epsilon Aurigae A few years ago, we told you about Epsilon Aurigae -- a star visible to the naked eye -- in the constellation Auriga. Once every 27 years this star fades in brightness for a period of nearly two years. Well, now it has faded and brightened again -- with astronomers looking on. We already knew that Epsilon Aurigae is really two objects -- a brilliant supergiant star -- and an invisible and generally mysterious companion. We also knew that the companion must pass in front of the main star at precise intervals of 27.1 years. But even during the eclipse -- when the whole system looks fainter -- some light from the hidden primary star still shines through to our eyes. Earlier theories proposed that the eclipsing object might be a semi-transparent shell of gas -- or a ring of gas which only partly covered the star. Either way the light of the primary star would fade -- but not entirely disappear. Modern observations -- made during the eclipse of 1982-83 -- call for a new model -- combining the two earlier ones. The invisible companion in Epsilon Aurigae may be a small hot star surrounded by a flat ring of dust, and several flat shells of gas. Surrounding that is an outer envelope of gas -- extending in a shell 10 times greater than the distance between our Earth and sun. A more complicated model -- but probably a better explanation -- to help us understand how a point of light in our night sky gets dimmer every 27 years. Script by Deborah Byrd. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin