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Cosmic rays and defective pixels removal

The ELODIE reduction software corrects the 2D frames from the cosmic rays (high energy particles hitting the CCD), and from the defective pixels (pixels with reduced sensitivity), with the optimal extraction method of Horne (1986). As the flux profile, perpendicular to the direction of dispersion, is known, the Horne's method corrects the pixels which do not match this profile.

But in the case of ELODIE, the width of the orders, perpendicular to the direction of dispersion, is very thin (3 to 5 pixels). In this case Horne's method misses a significant part of the cosmics and defective pixels (up to 200 cosmics detectable for a one hour exposure and $S/N \simeq 50$). To remove the remaining ``bad'' pixels, we are using three different and complementary methods on the 1D spectra. Figure 2 shows an order before and after cosmic rays and defective pixels removal.


  
Figure: Order 118 of HD 64090 ($T_\mathrm{eff}$ = 5446 K, $\log g$ = 4.45, [Fe/H] = -1.76, S/N = 106) before and after cosmic rays and defective pixels removal. Crosses flag cosmics detected by the flux method, circles flag cosmics detected by the regularity check method.
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\resizebox {8cm}{!}{\includegraphics{paper1fig2.ps}}\end{figure}



 
next up previous
Next: The flux method Up: Preparation of the spectra Previous: Flat field correction and

9/11/1998