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.
The Mysterious Epsilon
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.
2009 Epsilon Aurigae Campaign.
Stencel, R. E. , North American Workshop on the Recent Eclipse
of EPSILON AURIGAE , January 16-17, 1985, NASA Publications.
1985 Epsilon Aurigae Workshop Pictures