What are the advantages of a high resolution spectrometer?

    The high resolution spectrometer might be used to search for very small Doppler shift. The discovery of planets near stars has been done by careful measurements of Doppler shift. The high resolution spectrograph tends to be a large, heavy and sensitive piece of equipment.  At the Shane telescope the origional high resolution spectrometer was placed at the Coude focus of the telescope. The disadvantage of the Coude spectrograph is that it requires more light to detect the spectral lines. This is because the same light is spread across a longer color spectrum and because at the very long focal length a very narrow angle of the sky is overly magnified onto the spectrometer slit.  

The 'Automated Planet Finder' is to become operational at Lick Observatory during 2010.
The new short focus ~2 meter telescope will be more sensitive for its purpose than previous designs and will be used full time for extra solar planet search.

At the Keck Telescope the spectrograph is also used at a low F ratio.  
To have the high resolution with high sensitivity requires a very large diffraction grating.



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