This is an artists conception of binary star system TYC-2505-672-1. Credit: Jeremy Teaford, Vanderbilt University
Astronomers have discovered an unnamed pair of stars that sets a new record for both the longest duration stellar eclipse (3.5 years) and longest period between eclipses (69 years) in a binary system. Imagine living on a world where, every 69 yrs, the sun disappears in a near-total eclipse that lasts for over 3yrs. Nearly 10,000 light years from Earth the newly discovered system, catalog no. TYC 2505-672-1 was made by a team of astronomers from Vanderbilt and Harvard with the assistance of colleagues at Lehigh, Ohio State and Pennsylvania State universities, Las Cumbres Observatory Global Telescope Network and the American Association of Variable Star Observers..
The previous record holder is Epsilon Aurigae, a giant star eclipsed by its companion every 27 years for 640 to 730 days. It is closer at 2,200 light years from Earth – and brighter, which has allowed astronomers to study it extensively. Epsilon Aurigae consists of a yellow giant star orbited by a normal star slightly bigger than the sun embedded in a thick disk of dust and gas oriented nearly edge on when viewed from Earth. Prof. Keivan Stassun said: “Here we have a rare opportunity to study a phenomenon that plays out over many decades and provides a window into the types of environments around stars that could represent planetary building blocks at the very end of a star system’s life.”
2 unique astronomical resources made the discovery possible: American Association of Variable Star Observers (AAVSO) network and Digital Access to a Sky Century @ Harvard (DASCH) program. AAVSO is a non-profit organization of pro and amateur astronomers dedicated to understanding variable stars. It provided a few hundred observations of TYC 2505-672-1’s most recent eclipse. DASCH survey is based on thousands of photographic plates taken by Harvard astronomers between 1890 and 1989 as part of a regular survey of the northern sky.
The KELT robotic telescope database also provided 9,000 images of the obscure system taken in the last 8 years that they could combine with the 1,432 images taken over the last century at Harvard. The system appears to consist of a pair of red giant stars, one of which has been stripped down to a relatively small core and surrounded by an extremely large disk of material that produces the extended eclipse.
They were able to estimate the surface temperature of the companion star: ~2,000C, hotter than the surface of the sun. Combined with the observation that it appears to be less than half the diameter of the sun has led them to propose that it is a red giant that has had its outer layers stripped away and that this stripped material may account for the obscuring disk. However, they don’t know that for certain. To produce the 69-yr interval between eclipses, the astronomers calculate that they must be orbiting at an extremely large distance, about 20 astronomical units, approximately distance between Sun and Uranus. http://news.vanderbilt.edu/2016/02/longest-lasting-stellar-eclipse/
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