Helio- and Asteroseismology



When we observe the Sun, we can see many different oscillations at the same time, with different patterns over the solar disc. The more oscillations we can see, the more information about the interior we can get. Unfortunately we cannot yet resolve the distant stars into discs (with one or two very special exceptions using special imaging techniques) simply because they are so far away. Even in the largest telescopes stars are just single points of light, and therefore we obtain only the average of all the light emitted over the entire stellar surface. That means that most of that information on the patterns of node lines that we get for the Sun is not available. We only see vibrations that have very few node lines over the surface (or none at all). For the Sun we have measured over 100000 different oscillations, but it is only recently that we have succeeded in measuring oscillations on another star resembling the Sun - this feat was performed by researchers from Århus University ! Since we can see so many less modes we cannot find out as much about other stars as we can about the Sun. On the other hand, for other stars we normally only know the effective temperature and sometimes the luminosity or the mass. So measurement of even one or two frequencies of pulsation modes of a distant star doubles the amount of information we have on that star ! How well we have understood the physical conditions inside the stars is reflected by how good the models are that we make of them.

One of the biggest problems when observing starquakes, is the motion of air above the telecope (seeing) and other effects due to the earth's atmosphere. This is why we expect to do this kind of measurements from satellites sometime after the year 2000. This will make it possible to do much more thorough research into stars and their oscillations. At Århus University we are at the forefront of the research into starquakes and seismology of the distant stars and we expect to see many new results in this field in the coming years.