Seismic Studies of the global Sun with BiSON

The Sun is vital to life on Earth. Our research aims are to 'look' deep inside the Sun to help us understand how it works. Although you can't see it without special equipment, the Sun is shaking. Bubbling motion just under the visible surface of the Sun is constantly feeding in energy, and the Sun responds by vibrating just like a (very) large musical instrument. The 'notes' of the Sun's music are very interesting to astronomers. They are produced by sound waves which have travelled deep inside and their frequencies (the 'pitches' of the notes) depend on the conditions they meet on the way. For example, the frequencies depend on the density and temperature of the material inside the Sun and studying them allows astronomers to essentially get an 'ultrasound scan' of our nearest star. Actually turning these ideas into scientific reality is very difficult. The shaking of the Sun's surface is very small - it moves to and fro at a couple of metres per second (a slow walking pace), and takes about 5 minutes to go through a cycle. Just detecting this small movement takes specially designed instruments (called spectrometers, because they analyse the spectrum of sunlight). Some interesting effects on the Sun can last for several years. For example, there is a cycle of magnetic activity (which we don't fully understand yet) which makes the Sun have periods of 'spottiness' every 11 years or so. For this and other reasons, you would really like to observe the Sun's vibrations all the time over many years. One way of doing this is to have a number of robotic spectrometers in different sunny locations around the world, so that when the Sun sets on one instrument it has already risen on another. The Birmingham Solar Oscillations Network (BiSON) is just such a 'network' of spectrometers - there are 6 instruments in good sites for solar viewing in the Americas, Australia, Tenerife and South Africa. We designed and built these dedicated instruments, and we maintain and update them with local support and by visits by team members. The data are returned to our base in Birmingham via the Internet, and the remote link also lets us monitor the performance of the instruments and upgrade some of the software. Results from BiSON have been very important in helping astronomers to understand the Sun. The spectrum of the Sun's deepest vibrations was first detected by BiSON, and we continue to provide and analyse data which can help us to improve our understanding of everything from what makes the vibrations in the first place, all the way to information about the nuclear reactor at the Sun's core. Astronomers are beginning to measure the interiors of other stars, and our work on the Sun provides an important reference point for this new work. The effects we study are very subtle, and we spend much of our effort in analysing the data. To confirm that our results are 'real', we compare our results with those obtained by the small number of other astronomers who have similar equipment, and we also test our analysis programs on sophisticated artificial data sets which mimic as closely as we can the real thing. The beauty of simulated data is that you know exactly what went into them, so if you run your analysis programs you know what the output should look like. We have used simulated data for some years now, but as we have learned more about our instruments, we now know that there are several subtle effects which occur in real data that we've not yet built into our simulation programs. So our new proposal is to continue to maintain the BiSON network and collect high quality data. We will use these and other data to provide new information on the deep interior of the Sun (and inform the study of other stars), improve our understanding of the solar cycle and of the outer convective layers of the Sun where the vibrations are generated.