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Judi Lynn

(160,211 posts)
Sat Jun 15, 2013, 06:19 AM Jun 2013

Putting a new spin on variable stars

Putting a new spin on variable stars

Jun 14, 2013



Image of the open star cluster NGC 3766

Strange cluster of variability?

A new type of variable star has been discovered by astronomers in Switzerland. The team says that its observations reveal previously unknown properties of variable stars that defy current theories and raise more questions about the origins of the luminosity variation in stars. The team's results are based on a seven-year-long study of regular measurements of the brightness of more than 3000 stars in the open star cluster NGC 3766, using the European Southern Observatory's 1.2 m Euler telescope at the La Silla Observatory in Chile.

Variable stars are those with a brightness that appears to fluctuate or "vary" when they are observed from Earth. They are divided into two broad categories depending on the cause of the variation. If it is caused by a change in the physical properties of the star, then they are called "intrinsic variables", whereas "extrinsic variables" fluctuate thanks to external factors, such as an eclipsing orbiting companion. "Our group didn't know what would come out of the observations, but knew the potential of observing open clusters regularly on a long [period of time] to improve our understanding of known classes of variable stars...but none of us was expecting to find a new class," says Nami Mowlavi of Geneva Observatory, who is the current leader of the research team. Mowlavi says that the team's findings were so surprising that the researchers spent more than six months trying to understand and make sense of the results, but that ultimately "the quality of the data and of the analysis" convinced the researchers of the reality of the results.

Varying varieties

During the study, the team found 36 of the new variety of variable stars, which represent 20% of stars with similar magnitudes within the observed cluster. Mowlavi explains that these provide sufficient evidence of a new type because all the stars were observed in a single cluster. This means that they all have the same stellar properties, including their surface temperatures. Hence, what is so surprising about the results is that periodic light variations occur in stars with those specific temperatures.

"Were it only for their variability properties, these stars could have been considered as 'standard' variable stars, like some pulsating stars that are already known," says Mowlavi. But knowing that they are main-sequence stars – that burn hydrogen in their core, such as the Sun – with surface temperatures of between 9000 and 11000 K makes them very special. This is because main-sequence stars at these temperatures are not expected to pulsate, or to have any other physical characteristic that would lead to periodic variations of their luminosity, according to current theories.

More:
http://physicsworld.com/cws/article/news/2013/jun/14/putting-a-new-spin-on-variable-stars

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