"Another new field of astronomy to come of age during the 1980s has
been the discipline of helioseismology, or studying the internal
structure of the Sun by measuring its modes of oscillation. Solar
oscillations of about a five minute period probe a wide range of
different depths into the Sun and have enabled its detailed internal
structure to be defined with quite remarkable precision. For example,
the variation of the speed of sound with radius is now known to better
than 1% throughout the Sun. These studies can be extended to nearby stars
using the 8-meter telescopes with very high resolution spectrographs.
For the first time, it will be possible to infer directly the internal
structures of stars other than our own Sun."
-Dr. Malcolm S. Longair, Chair of the Gemini Board 1994-1995
What is the internal structure of the stars? The characteristics of
the sound waves trapped within the photosphere of a star are critically
constrained by the star's physical structure, with the many different
waves causing a complex oscillation of the visible surface. The "five
minute" oscillations of the Sun have set important limits to the size
and structure of its photosphere and internal rate of rotation. The
velocity amplitudes associated with the oscillations are subtle, less
than 1 m/s, non-repetitive, and they must be monitored for many hours.
With Gemini's light gathering power and a spectrograph
of sufficiently high resolution, it will now be possible to probe the
interiors of nearby main sequence stars in an analogous fashion to the
Sun.
Image Credits: 1:NOAO
Ruth A. Kneale / web@gemini.edu / February 27, 1998