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Friday, 09 April 2010 01:07

Star epsilon Aurigae mystery looks to be solved


Once every 27 years astronomers see a mysterious object passing in front of the star epsilon Aurigae. Based on new images taken in January 2010 when the star was fully eclipsed by this mysterious object, astronomers now think the object is another star with a dusty disk around it.


Epsilon Aurigae, a yellow supergiant star in the constellation Auriga (the charioteer), is about 2,000 light-years away from Earth.

For the past 190 years or so, since the 1820s, astronomers have seen a mysterious object travel in front of epsilon Aurigae, what scientists call eclipsing the star (and what happens when we see the moon go in front of the Sun, or vice versa).

In 1821, German astronomer Johann Fritsch was the first astronomer to see the dimming (variability of light) of epsilon Aurigae.

Then, in 1937, three astronomers, Gerard Kuiper, Otto Struve, and Bengt Strömgren, suggested in a published paper that the mysterious object and epsion Aurigae were two members of a binary system.

This binary-disk hypothesis is one of several hypotheses brought forth on the mystery surrounding the star.



Astronomers have hypthosized that the mysterious object could also be a black hole, a dusty nebula, or (as earlier stated) another star, with a dusty disk around it, in a binary system with epsilon Aurigae.


Page two continues.


Read the article 'The 'Star' of Our Project' for more information about the mystery surrounding the star epsilon Aurigae.

During this time of being eclipsed, the brightness of the star epsilon Aurigae (also called Haldus, Al Anz, and Almaaz) drops from an apparent visual magnitude of +2.92 to +3.83.


As apparent magnitude decreases (increases) within a star (from our point of view on Earth), the number gets larger (smaller), as shown here.

This dimming of the star, which happens once every 27 years, lasts from about 640 days to 730 days.

An illustration of this mysterious object eclipsing epsilon Aurigae is found on the National Geographic website 'Yearlong Star Eclipse May Help Solve Space Mystery.'

Based on these images, astronomers now think that the binary-disk hypothesis may be the correct one.

Page three continues.


The images taken of the star epsilon Aurigae is published in the April 8, 2010 issue of the journal Nature. And, the images 'seem to confirm the binary-disk theory.'

The Nature paper's title is 'Infrared images of the transiting disk in the ϵ Aurigae system.'

Its authors are Brian Kloppenborg, Robert Stence, John D. Monnier, Gail Schaefer, Ming Zhao, Fabien Baron, Hal McAlister, Theo ten Brummelaar, Xiao Che, Chris Farrington, Ettore Pedretti, P. J. Sallave-Goldfinger, Judit Sturmann, Laszlo Sturmann, Nathalie Thureau, Nils Turner, and & Sean M. Carroll.

They state, 'Epsilon Aurigae (ϵ Aur) is a visually bright, eclipsing binary star system with a period of 27.1'‰years. The cause of each 18-month-long eclipse has been a subject of controversy for nearly 190'‰years because the companion has hitherto been undetectable.'

And, 'The orbital elements imply that the opaque object has roughly the same mass as the visible component, which for much of the last century was thought to be an F-type supergiant star with a mass of ~15M⊠(MâŠ, mass of the Sun).'


Page four concludes.



Further, 'Here we report interferometric images that show the eclipsing body moving in front of the F star. The body is an opaque disk and appears tilted as predicted. Adopting a mass of 5.9M⊠for the B star, we derive a mass of ~(3.6'‰±'‰0.7)M⊠for the F star."


In conclusion, "The disk mass is dynamically negligible; we estimate it to contain ~0.07ME (ME, mass of the Earth) if it consists purely of dust.'

The National Geographic article indicates that the supposed disk, according to U.S. astronomer Robert Stencel, from the University of Denver (Colorado), and one of the authors of the Nature paper, is "a much longer, thinner cigar than most artists tend to illustrate.'


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