Helio- and Asteroseismology


Asteroseismology at Århus University

More than 20 years ago it was discovered that the Sun continually oscillates - the so-called solar oscillations or Sun-quakes - that on the solar surface look like a complicated system of waves. By measuring thousands of such Sun-quakes we have been successful in studying the solar interior. In the same way that geologists have researched the Earth, astronomers in the past 20 years have built up a very detailed picture of the physical conditions under the solar surface, conditions that cannot be observed directly. In this time many of our ideas about the details of the internal structure of the Sun have had to be revised, which of course has led us to speculate to what extent our insight about the interior of other stars is correct.

This is why astronomers in the past 10 years have attempted to find waves or oscillations (starquakes) on other stars than the Sun, through which we would hope to have the possibility to perform detailed research of the interior of stars - something that has never been done before. Astronomers at Århus University are very active in this research, but the work isn't nearly as straightforward as studying solar oscillations. The periodic wave movements, that arise from starquakes and Sun-quakes are almost impossible to measure. Even for observations of the Sun, which is 10 billion times brighter than the brightest star, very special equipment is required to measure the relatively small wave motions.

Researchers of Århus University and the European Southern Observatory (ESO) attempted in 1994 to measure starquakes on the star Eta Bootis (which is also called Mufrid), which can be seen in the northern sky in the constellation of (Bootes) close to the bright red star Arcturus. Eta Bootis is about 38 lightyears distant from Earth and is a yellow star with a diameter about 3 times that of the Sun. The Nordic Optical Telescope (NOT) on the small island La Palma - one of the Canary islands - was used for the observations in April 1994. Observations done in the course of 6 clear nights led to the discovery of what is probably starquakes of the same type that we know occur on the Sun.