Epsilon Aurigae


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Epsilon Aurigae

(ô-rÿ -jee, -ree -) An eclipsing binary star about 600 parsecs distant in the constellation Auriga, with a period of 9892 days, the eclipse lasting about 610 days. It consists of an extremely luminous F2 Ia supergiant about 15 times the mass of the Sun with a very large companion of about the same mass. Once thought to be a very distended cool supergiant, the large occulting object is now believed to be a ring or shell of gases surrounding the true companion, a main-sequence B star. The gases arise from rapid mass transfer from the F star (see W Serpentis star).
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Ever since the star's periodic eclipses were first recorded in 1821, astronomers have been puzzling over how Epsilon Aurigae pulls off its lengthy disappearing act.
Genet of Fairborn (Ohio) Observatory point out, "Epsilon Aurigae, because of both its brightness and the long duration of its eclipse, is a difficult photometric object for large telescopes at major observatories, but for the same reasons it was ideally suited for small telescopes at the smaller observatories."
Using the International Ultraviolet Explorer satellite in 1979, Margherita Hack (University of Trieste, Italy) found a clue when she took the first ultraviolet spectrum of Epsilon Aurigae. She argued that the system's unexpectedly high ultraviolet brightness requires a relatively massive star inside the disk.
During Epsilon Aurigae's 1980s eclipse, the UBV bands were most popular.
Sensitive electronic imagers have replaced film and amateurs have recently developed spectrographs capable of resolving spectral lines just a few hundredths of a nanometer wide, sufficiently high resolution for pro-am collaborations such as the Epsilon Aurigae campaign.
The international variable star community has been waiting expectantly for the eclipse of the Epsilon Aurigae system.
Epsilon Aurigae's polarization had first been studied during the 1982-84 eclipse, and Dr.
August 6 sees the predicted start of the eclipse of Epsilon Aurigae (see also p.219).
The Citizen Sky project is a focused effort by the American Association of Variable Star Observers (AAVSO) to coordinate observations of Epsilon Aurigae's 2009-11 eclipse and also promote amateur use of the data they collected.
But this issue's articles about Epsilon Aurigae give me some reason for optimism that the Golden Age might continue in spite of the perfect storm.
Amateur Jeff Hopkins, a renowned observer of Epsilon Aurigae, organized nearly 60 amateur and professional astronomers in a worldwide observing campaign for the current eclipse (www.hposoft.com/Campaign09.html).