Stellar Girocronologia

It is very difficult to measure the changes in brightness as they are typically less than 1% and can take several days before a spot crosses the stellar disk. However, researchers have achieved the exploit thanks to the extremely sensitive observations made by NASA’s Kepler who provided continuous and accurate measurements of the brightness of stars. It is very difficult to derive the age of a star very old because it rotates more slowly and has dark spots smaller and weaker.
In order for the ages obtained by the technique of girocronologia are precise and accurate, astronomers must calibrate their new watch obtaining measures of the rotation period for those stars with known age and mass. In the past, researchers have studied a star cluster whose components have about 1 billion years. In this work, the scientists looked at the stars in NGC 6819 that has an age of 2.5 billion years, so I extend in a rather significant interval of age.


Credit: David A. Aguilar (CfA)

“The older stars have a few dark spots and smaller, making it difficult to measure the rotation period,” says Meibom. The researchers analyzed a set of stars that have a mass of 80-140% that of the sun. In addition, they have measured the spin of 30 stars who have a period of between 4 and 23 days, compared to that of our star that is 26 days. The 8 most stars similar to the Sun, present in the cluster NGC 6819, have a rotation period average of 18.2 days, which strongly implies that the rotation period of the Sun had to have that value about 2 billion years ago.
The scientists then evaluated several numerical models which allow calculating the rotation period of the star from the mass and age, to find out which model is closer to the data obtained from their observations. “Now we are able to derive very accurate values of the age for a large number of stars belonging to our galaxy, thanks to the extent of their period of rotation. It is a new, important research tool that astronomers can use not only to study of the evolution of the stars but also to identify those planets evolved enough where there may be quite complex forms of life”, concludes Meibom.
In short, these results represent the first attempt at such an approach applied to the stars that are older than 1 billion years and extend to objects that have 4.6 billion years, the age of our sun. Being able to determine the age of the stars is a key point to understand how the astronomical phenomena that affect the stars and their partners will be revealed over time. Since the stars and planets are formed together and at the same time, to derive the age of the central star indirectly involves knowing the age of the planets. And as life needs time to evolve and develop to reach that complexity we see today, know the age of the host stars can help astronomers narrow the field of candidates to look for any alien life forms. Therefore, with a clock stellar fairly accurate, scientists will be able to identify those stars peers or older than the Sun where there is possibly a planetary system.

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