Space

Gyrochronology, a New More Effective Method of Determining the Stars' Age

It uses the rotation period and color of the stars

By Stefan Anitei, Science Editor

27th of April 2007, 09:57 GMT

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The age of a star says a lot about its traits, that's why this is one of the first goals of the astronomers when they detect a new one.

"The ages of the host stars of planetary systems are needed to understand how these systems change over time," said Sydney Barnes, from Lowell Observatory.

Till now researchers used the isochrone and chromospheric techniques. Isochrone ages measure the evolutionary records of the stars, effective for star clusters, but they do not work well for individual (field) stars as the distances must be measured also for stars on the main sequence, where the majority of a star's life is spent. Chromospheric ages employ the measured chromospheric emission from stars but have significant uncertainties, up to 50 %.

Now Barnes comes with gyrochronology, a method that finds the ages of field stars based on their rotational rates.

"Gyrochronology transforms a rotating star into a clock which is set using the Sun and keeps time well".

Gyrochronology determines the age by assessing the two other properties - the rotation period and the color.

"If you know the relationship between three quantities, measuring two of them allows you to calculate the third," said Barnes.

"The relationship between age, color, and rotation period has particular and useful mathematical properties that simplify the analysis and allow the uncertainties to be calculated easily."

A star's color is linked to its mass or surface temperature.

Gyrochronology ages have uncertainties of about 15 %, with the other methods of 50 to 100 % and can be tuned with the known age of the Sun (4.6 billion years). This technique is effective for most stars, including field stars and is extremely accurate for sun-like and low mass stars that use hydrogen as fuel at a steady rate (named main sequence)

Barnes's research points that the rotation period of a star (whether in a cluster or in the field) is the product of two separable functions of its age and color.

Gyrochronology managed to prove that the individual components of three wide binary stars have essentially the same ages but, by now, is not very effective for the youngest stars, which have not begun burning fuel at the steady rate or for those that have left the main sequence.

TAGS:

star | rotation | color

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