The nature of the fiber noise with the FOCES spectrograph

Nature, modeling and a way to achieve S/N  

Universitäts Sternwarte München, Scheinerstr. 1, 12345 München, Germany

Corresponding author: fug@usm.uni-muenchen.de

Received: 15 April 2003
Accepted: 8 September 2003

Abstract

The non-white noise noticed using the fiber-fed Foces spectrograph is recognized as the result of vignetting to an uneven distribution of monochromatic light in the spectrograph beam behind the fiber exit. This phenomenon – that can be assigned to every fiber-coupled spectrograph with vignetting of the light path behind the fiber – is qualitatively and quantitatively described and modeled. The  ratio that seemed to be limited to ≈200 when surrounding the object exposure by two flatfield exposures is shown to reach the theoretical limit (defined by the linear range of the CCD-detector) of . This is achieved by using multiple flatfield exposures in combination with a fiber vibration device allowing non-harmonic movement of the fiber during exposure time.