The Tools We Need To Do Our Research
In order to investigate solar oscillations the group conceived, built and currently operates a global network of observatories dedicated to the continuous observation of the Sun.
Each station is equipped with an array of sophisticated instruments. The main devices that are used by the group are resonant-scattering spectrometers. These devices work in a different manner to the more familiar grating spectrometer. The resonant-scattering component within our spectrometers consists of a small silica vapour cell, containing an ensemble of potassium atoms heated to ~100 oC, so that they form a vapour. The cell is held in a strong magnetic field that moves the working parts of the vapour into the blue and red wings of the Solar Fraunhofer Line. The assembly on either side of the cell focuses resonantly-scattered light onto two solid state detectors. This arrangement is shown schematically below:
Photodetectors or photomultiplier tubes are used in the BiSON instruments to measure the intensity of light scattered from a small, glass cell containing potassium vapour. These devices output a voltage proportional to the intensity of the light falling on their active surfaces. The output voltage is passed through a voltage-to-frequency (V/F) converter and the resulting pulses are routed to a set of counters where they can be subsequently processed.
The polarization of the incoming light is controlled by special electronics. The same hardware also sends the appropriate gate signals to the counters. For each sample the counter gates are held open for 3.2 seconds. The gates are then closed for 0.8 seconds to allow the readout electronics to read the accumulated counts from the counters. In this way, one line-of-sight measurement of the Sun is taken every four seconds.
Data Transfer and Preprocessing
In order to save CPU time, the four-second data collected throughout the day is written directly to a raw data file. At sunset some compacting software reads this file, performs some statistical analysis on the data and then writes out a daily file that contains data in a forty-second format. The daily data is transferred from the remote stations to Birmingham either across a modem link or via the internet.