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Stellar Seismology

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Stellar Seismology .... Looking into a star by listening!


Helioseismology and Asteroseismology are the terms for investigating our sun and other stars using seismology.

Stellar Seismology is a way to see inside the stars.
Its principle is to detect and measure the features of a star through detection of acoustic oscillations and to use these characteristics to understand the inner structure of a star.

These types of measurements have been used for a long time on the Earth to help understand the inner structure of our planet.

It can now allow us to determine the interior structure of stars by interpreting the frequency spectrum.
This is the only way currently existing to know more about the deeper stellar interiors.


http://gong.nso.edu/gallery/images/harmonics/modes_lg.jpg
Sound is produced by pressure fluctuations and have pressure as a restorative force, so detection using these vibrations or oscillations is done via p modes.

Of course we can't detect the actual sounds made by the sun - there's no propagation of sound waves through space - but we can detect them through the small amount of blue and red shift that is seen in the spectrum of the surface of the sun.

A map of the sun's oscillations, show areas that are moving away from us or into the sun (in red) and outwards from the sun (in light blue).

These waves or pulsations are caused from within the sun.
A vibration with a period of about 5 minutes is strongest.

Different probing methods can be used to target different layers or depths of the star.

f modes are fundamental vibrations caused by surface gravitation and are only found in the outer layer.

p modes are caused by pressure and are restricted to near the surface of the star down to just into the radiative zone.
Using various p modes allows us to investigate different depths.

g modes are caused by internal gravitation deep within the core and have the potential to detail the deep interior of the sun.


http://gong.nso.edu/gallery/images/harmonics/cut-away.jpg

Helioseismology isn't just theoretical. It has been used to detect the flow of gas currents under the photosphere (beyond our optical viewing) and to detect the emergence of a sunspot before it surfaced. Even sunspots on the far side of the sun have been detected through helioseismology.

Stellar Seismology helps to determine chemical compositions, density, rotations, convective zone depth, internal temperature, magnetic fields as well as other internal structures.






Some references & resources:-
Why stars aren't like sheep.
Heliowhat ?
Wikipedia entry for heliosiesmology
NASA - Marshall Space Flight Centre
Solar Music - for younger children
GONG
Stellar Seismology and COROT
BiSON
helioseismology
Cepheids
Helioseismology
Seismology links






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02/05/2007