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Old nova sparks a new theory.

The astronomical term "nova" comes from the Latin phrase stell nova, new star, which old-time astronomers applied to the sudden appearance of a bright star where they had seen none before. After the invention of telescopes, astronomers found out that these phenomena are explosions that happen to starts that were always there but were sometimes invisible to the naked eye. Unlike supernovas, which essentially blow the whole star away, ordinary novas may recur. However, because recurrence is a matter of millenia, astronomers studying the evolution of novas must look into the astronomical records of the past. Three astronomers ahve now "recovered" -- that is, found -- the star responsible for a conspicuous nova of the year 1670. The observation leads them to suggest that a nova's life cycle is much longer than astronomers have thought.

The three astronomers, Michael M. Shara of the Space Telescope Science Institute in Baltimore, Anthony F.J. Moffat of the University of Montreal and Ronald F. Webbink of the Joint Institute for Laboratory Astrophysics in Boulder, Colo., point out in the July 1 ASTROPHYSICAL JOURNAL that the first to note the 1670 nova was apparently the Carthusian monk Pere Dom Anthelme of Dijon, France. Shortly afterward a famous astronomer of the period, Johannes Hevelius of Danzig (now Gdansk, Poland), found it. The nova is listed in contemporary records as nova sub capite cygni, the nova under the head of the swan. But it is now called CK Vulpeculae, for the constellation vulpecula cum ansere, the little fox with the goose. It is the oldest nova yet recovered, Shara says.

From the 17th-century records Shara, Moffat and Webbink determined the position of the nova as right ascension 19 hours 45 minutes 32.41 seconds and declination +27[deg.] 11' 22.6". There they found a very faint star surrounded with bright matter that looks like ejecta. From the geometry of the ejecta, they determined that some of them had been thrown out in the plane of the star's equator and some off the pole. The first surprise was that the central star is much fainter (magnitude 10.4) than expected from the generally accepted theory, which is based on more recent novas--"100 times fainter than any other nova," says Shara.

The three observers then used the old records to determine a light curve, a graph of brightness over time for the nova during its conspicuous period. With nothin as exact as modern photometric measurements, they had to interpret such terms as obtusior, duller or blurred, and rubicundior, ruddier. The result shows that the nova was conspicuous for an exceptionally long tiem (three years) and its peak brightness varied a lot.

According to accepted theory, a nova is a binary star system containing a white dwarf and a more ordinary star. They are so close together that matter is pulled from the companion star by the white dwarf's gravity. The inflowing matter eventually causes an unstable condition, and the white dward explodes, blowing away the excess. Immediately the flow of matter starts again, building up to another explosion. Not so, say Shara, Moffat and Webbink. Instead, they say, the explosion separates the starts, stopping the matter flow for a while. Eventually the starts move back together as they lose angular momentum through gravitational radiation or magnetic interactions, and then the matter flow starts again. The difference leads Shara, Moffat and Webbink to suggest that the time between nova explosions is more like 100,000 years than the 1,000 to 10,000 postulated by accepted theory.
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Title Annotation:CK Vulpeculae
Author:Thomsen, Dietrick E.
Publication:Science News
Date:Aug 3, 1985
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