'Ringing' of star leads astronomers to find its birthplace

Munich, April 16 : A team of astronomers using ESO's (European Southern Observatory) 3.6-m telescope have studied the 'ringing' of a planet-harbouring star, and have thus found its place of origin.

According to the astronomers, the yellow-orange star Iota Horologii, located 56 light-years away towards the southern Horologium ("The Clock") constellation, belongs to the so-called "Hyades stream", a large number of stars that move in the same direction.

Previously, astronomers using an ESO telescope had shown that the star harbours a planet, more than 2 times as large as Jupiter and orbiting in 320 days.

But until now, all studies were unable to pinpoint the exact characteristics of the star, and hence to understand its origin.

A team of astronomers, led by Sylvie Vauclair from the University of Toulouse, France, therefore decided to use the technique of 'asteroseismology' to unlock the star's secrets.

As to how this technique functions, Vauclair said that "In the same way as geologists monitor how seismic waves generated by earthquakes propagate through the Earth and learn about the inner structure of our planet, it is possible to study sound waves running through a star, which forms a sort of large, spherical bell."

The 'ringing' from this giant star provides astronomers with plenty of information about the physical conditions in the star's interior.

To 'listen to the music', the astronomers used one of the best instruments available.

The observations were conducted in November 2006 during 8 consecutive nights with the state-of-the-art HARPS spectrograph mounted on the ESO 3.6-m telescope at La Silla.

Up to 25 'notes' could be identified in the unique dataset, most of them corresponding to waves having a period of about 6.5 minutes.

These observations allowed the astronomers to obtain a very precise portrait of Iota Horologii: its temperature is 6150 K, its mass is 1.25 times that of the Sun, and its age is 625 million years.

Moreover, the star is found to be more metal-rich than the Sun by about 50%.

According to Vauclair, these results show that Iota Horologii has the same metal abundance and age as the Hyades cluster and this cannot be a coincidence.

The star Iota Horologii must have thus formed together with the stars of the Hyades cluster but must have slowly drifted away, being presently more than 130 light-years away from its original birthplace, he added.

This is an important result to understand how stars move on the galactic highways of the Milky Way.

ANI