Asterosismology

In Astrophysical, the asterosismology is the discipline which studies the seismic movements (also called oscillations) of the star S other than the Sun (in this case, one speaks about Héliosismologie). The asterosismology is a technique of study of the internal structure of stars.

History

Whereas the seismology of the Sun knows its golden age, stellar seismology is still quite young. Although the discovery of the pulsation of stars goes back to the end of the 18th century (the Céphéide S used to gauge measurements of galactic distances), it is only very recently, in 2000, that the detection of oscillations similar to those of the Sun in another star was confirmed. Following many successes of seismology to probe the solar interior, the asterosismology knows since a significant development with in particular the space missions MOST, CoRoT or the project of network of telescopes on the ground SONG. Many stars, covering a broad field of masses, ages, stages of evolution, are known to have oscillations. The challenge is to be able to measure to them Frequency spectrum with sufficient precision and of resolution to deduce from them the best information on their structure and the physical processes which live them.

Stellar oscillations

There exist various mechanisms of excitation of the stellar oscillations, for example related to the variations of the Opacité influencing the transport of energy, or related to the violent ones movements convectifs on star surface of the solar type. Thus various types of waves can be excited. In the case of the Sun, and of similar stars, violent ones movements of convection to work in the surface layers, which result in the granulation observed on its surface, excite sound waves. The various types of waves being propagated in and on the surface of the Sun are:

modes of Pressure: they are acoustic waves, oscillations whose force of recall is the pressure of gas. These modes are generated in the convective zone by the turbulent convection of surface. They are propagated through all star, of surface in the middle, and their trajectory is determined by the variations speed of sound.
modes of Revolved: oscillations whose force of recall is the Poussée of Archimedes. They are confined in the radiative zone but are évanescents in the convective zone, which makes their detection very difficult on the surface where they reach a very low amplitude (a few m/s). This explains why they are not detected yet without ambiguity. They are essential to be able to explore in detail the structure and the dynamics in the heart of the Sun, where the use of the modes p reaches its limits.
modes “F”: they are modes showing the same characteristics as a wave of gravity of surface (like waves). They are used to probe the surface areas of the Sun.

The amplitude of the oscillations plays a big role in their detection and their measurement, and imposes more or less severe constraints on the conditions of observation. The stars of the solar type presenting of the oscillations of very low amplitudes require continuous observations and long lives to leave a spectrum good quality, with a sufficient resolution and a precision to estimate the characteristics of the spectrum.

See too

Héliosismologie
Seismology
Tremor of star

External bonds

stellar seismology on the site of the Laboratory of space studies and instrumentation in astrophysics, of the Observatory of Paris
Internet site dédidé with the asterosismology
, the site of mission COROT
the course of J. Christensen-Dalsgaard on the seismology of the stars
the course of B. Mosser on seismology and the structure of the stars

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