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TOPIC: Epsilon Aurigae


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RE: Epsilon Aurigae
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Almost directly overhead in this month's Colorado sky is the prominent yellowish-white star called Capella.
Situated in the pentagon-shaped constellation of Auriga the Charioteer, Capella is the sixth-brightest star in the night sky and with its companion stars constitutes a system interesting enough to have been a past topic for this column.
This month, however, we journey to the south of Capella where we find a small "skinny triangle" asterism of moderately bright stars named the "Goat Kids." The apex or spear point of this triangle is occupied by one of the most interesting objects in all of stellar astronomy, a star called Epsilon Aurigae.

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Observers are reporting visual magnitude approaching 3.4, which is half-way between the out of eclipse average, close to 3.0, and the anticipated magnitude during totality, 3.8.

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Epsilon Aurigae has started to dim.
The eclipse of the mystery star Epsilon Aurigae in the constellation Auriga has begun.
The lightcurve shows a drop from magnitude 3.0 to magnitude 3.25, which should continue over the next few months to drop to magnitude 3.8 or more at which point it will stay dimmed for nearly a year.

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The mysterious epsilon Aurigae eclipse
Something strange is afoot 2,000 light years away in the constellation Auriga. Every 27 years one of its stars dims significantly, eclipsed by a perplexing disk 930 million miles wide and one-tenth of that in height.


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Epsilon Aurigae: mystery star
In the far northern constellation of Auriga the Charioteer, not far from the bright star Capella, an astronomical mystery is about to play out, as it has every 27 years for the past century. Professional astronomers and citizen astronomers worldwide are watching and waiting for the star Epsilon Aurigae to begin to fade during August. Epsilon Aurigae is an eclipsing binary star, not in and of itself very unusual, but the object that is creating the eclipse remains one of the most puzzling of astronomical mysteries.

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Epsilon Aurigae, the long-period eclipsing binary star is predicted to begin its next eclipse by late July or early August, 2009.
The magnitude +3.0 star will dim to magnitude +3.8 as some unknown object passes in front of the star.
The period is 27.12 years.
The 6th August is the predicted start of eclipse. During August, the star will rise as a morning star.
The predicted end of the eclipse is on the 15th May, 2011.

Position(2000): RA 05:01:58.13 , Dec +43:49:23.9

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No one likes it when a light bulb dims and then brightens on its own. When a star acts like it has a dimmer switch, astronomers -- professional and amateur alike -- are fascinated. There are a variety of causes for a star to vary, but one star in particular is a long-standing mystery. The star is known as Epsilon Aurigae, which on our star maps marks the nose of Auriga the Chariot Driver.

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The peculiar variable star, epsilon Aurigae, lives within a cosmic context. Since the beginning people have looked at the night sky with wonder. At first glance it appeared the nigh sky was fixed except for the Moon's movement. The points of light we know as stars were thought to be embedded in a celestial sphere. The Greeks were the first to devise a system for determining the brightness of the stars. While they used a system of just six magnitudes it was at least a start. A magnitude 1 star was considered the brightest they could see while magnitude 6 was the faintest, 100 times fainter in fact. We now know there are stars much brighter than magnitude 1 (our Sun is a star and is magnitude -26.8, Sirius, the brightest star in the night sky is magnitude -1.47 and Vega is magnitude 0.03) There are also billions of stars fainter than magnitude 6. One must remember that the lower the magnitude number and extending into negative numbers, the brighter the star. A magnitude -2 is many times brighter than a magnitude +2 star.

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Title: Interferometric Studies of the extreme binary, $\epsilon$ Aurigae: Pre-eclipse Observations
Authors: R.Stencel, M. Creech-Eakman, A. Hart, J. Hopkins, B.Kloppenborg, D.Mais

We report new and archival K-band interferometric uniform disk diameters obtained with the Palomar Testbed Interferometer for the eclipsing binary star epsilon Aurigae, in advance of the start of its eclipse in 2009. The observations were intended to test whether low amplitude variations in the system are connected with the F supergiant star (primary), or with the intersystem material connecting the star with the enormous dark disk (secondary) inferred to cause the eclipses. Cepheid-like radial pulsations of the F star are not detected, nor do we find evidence for proposed 6% per decade shrinkage of the F star. The measured 2.27 0.11 milli-arcsecond K band diameter is consistent with a 300 times solar radius F supergiant star at the Hipparcos distance of 625 pc. These results provide an improved context for observations during the 2009-2011 eclipse.

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