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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 ).
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 ( = 5446 K, = 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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Next: The flux method
Up: Preparation of the spectra
Previous: Flat field correction and
9/11/1998