Helio- and Asteroseismology


Starquakes on Eta Bootis.

In 1994 researchers from Århus University used the Nordic Optical Telescope on La Palma to look for oscillations on the star Eta Bootis

In total 13 different oscillations or quakes were observed on the star, and the periods of the oscillations are around 20 minutes. Seismological research shows that Eta Bootis has a mass about 60% larger than that of the Sun. Its internal structure is quite different from the Sun because Eta Bootis can no longer produce energy in the core by converting hydrogen to helium, like the Sun does. Eta Bootis has used up its supply of hydrogen and is in the process of developing into what is known as a red giant star. This is happening at this moment, which means among other things that the inner parts of the star are slowly contracting. This slow contraction of the core causes the temperature in the center to increase, while at the same time the star as a whole expands. In a narrow shell around the core there is still production of energy by conversion of hydrogen to helium, but it can no longer occur in the core. Apart from this the seismological data seem to show that the turbulent part of Eta Bootis - the so-called convection zone - does not resemble closely similar layers in the Sun.

More extensive studies of the oscillations will yield an even more detailed picture of the conditions in the stellar core. The first results seem to confirm the common assumptions about conditions in stellar cores, and only some details must be corrected.