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SONG explained

The SONG telescope

The telescope has a diameter of 1m and is located at the Observatorio del Teide on Tenerife. A small aperture telescope is sufficient to obtain data of the required quality, as the purpose of SONG is the study of bright stars, those you can see with your naked eye. The telescope is built by the German company ASTELCO Systems GmbH.

The SONG spectrograph

A spectrograph is an instrument that separates light into its different colours, operating in a manner not unlike the droplets of rain that create a rainbow. Light from distant stars enters the spectrograph and will be spread out into all the different colours, allowing us to study them individual. The colours (or wavelengths) carry information about the stars and can be used to determine their mass, size and chemical composition, among other things.

The picture to the right shows how the output (a spectrum) from the spectrograph looks. Numerous dark lines can be seen. These are called spectral lines. By making very precise measurements of their position, we can determine the surface velocity of the stars we observe through the Doppler effect.  We can measure the velocity to a precision of 1-2m/s, which corresponds to a shift of ~100 atoms in the position of the spectral lines on the digital camera in the spectrograph.

 

 

The SONG Lucky Imaging cameras

Lucky imaging is a technique to remove the smearing effect the atmosphere causes of stars on images. The changes in the atmosphere occur very quickly, over timescales on the order of milliseconds. Modern CCD cameras can acquire images as fast as 10 times a second. By sorting out the images that are most affected by the atmosphere and keeping only the sharpest, it is possible to combine them and create a sharp image with a long effective exposure time.

Web cameras

For images showing the node at the first site at Tenerife check the Webcam 1 or Webcam 2.