Epsilon Aurigae

Epsilon Aurigae Star System

The epsilon Aurigae system is perhaps the most interesting eclipsing star system. It has puzzled astronomers for over 150 years. It is a bright star (3rd magnitude) located about 3 degrees southwest of Capella and eclipses once every 27.1 years. It is at the vertex of a triangular group of stars known as "The Kids". Zeta Aurigae, another interesting long-period eclipsing binary, makes up one of the other two stars. See: The Mysterious Epsilon Aurigae.

What makes this star system so intriguing is not just its long period but the length of its eclipse and what happens during the eclipse. Typically the eclipse lasts about two years which with the 27.1 year period means the eclipsing body must be gigantic. There have been no satisfactory explanations for this. To make matters even more interesting, there seems to be a mid-eclipse brightening. How can this be? One explanation, according to James Kemp, is the eclipsing body is a giant cloud of gases enclosing two small stars in orbit around each other. These stars sweep out an area in the middle. It would be a bit like a giant donut. This donut must be tilted such that as it eclipses the primary star, the system's total light decreases until the "donut-hole" allows some of the primary star's light to sneak through at mid-eclipse.

To try to unravel this system's mystery, a concentrated effort was undertaken during the 1982-1984 eclipse. Hundreds of astronomers, amateurs and professionals, from around the world, observed the eclipse. Space born satellites observed in the ultraviolet and infrared. Ground based observations were photometric, spectroscopic, and polarmetric. Photometric observations were made with UBV filters, narrow band filters, and at wavelengths into the far infrared. Despite the concentrated efforts, epsilon Aurigae still remains a mystery. The secondary eclipse was due to occur around 1996/1997. Because the secondary eclipse light variation is on the order of the primary star's pulsations, it will be difficult to separate the two. An effort is underway to try to predict the pulsations through continuing observations. If these pulsations can be predicted, observation of the secondary eclipse may be possible.

For those astronomers still interested, while the next eclipse willl start in the early spring of 2009, now will be a good time to start a new campaign to obtain out-of-eclipse observations before the next eclipse. Epsilon Aurigae is anything but quiet out-of-eclipse. Surely, by the end of the next eclipse, astronomy will have unraveled the mystery of epsilon Aurigae.

The 2009 Epsilon Aurigae Campaign.

Reference: Stencel, R. E. , North American Workshop on the Recent Eclipse of EPSILON AURIGAE , January 16-17, 1985, NASA Publications.

See 1985 Epsilon Aurigae Workshop Pictures

Epsilon Aurigae System Diagram

Epsilon Aurigae Basic Star System Data

Epsilon Aurigae Star Chart

Data and Plots

V Data Plot 1982 - 1984

V Data Plot 1984 - 1988

UBV Data 1982 To 1988
Includes 1982 - 1984 Eclipse Data

Photometric Data
December 2003 - April 2005

2004 - 2005 Spectra of Epsilon Aurigae
provided by
Dr. Dale Mais and
Dr. Lothar Schanne


1982 -1984 Eclipse Campaign

Epsilon Aurigae IBVS References

Epsilon Aurigae References
Photometric, Spectroscopic and Interpretation

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Is the eclipsing variable EE Cep
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Created 6 October 1996
Modified 25 July 2005