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From the download field, the user can obtain two types of FITS files, the whole resampled spectrum and the s2D FITS files:
This archive is actively maintained. We thus welcome feedback from the user
to help us detect anomalies and improve the website.
- The whole spectrum FITS file (spec button) is resampled in wavelength and is given in instrumental relative flux. For more details about this procedure please refer to the description of the full reduction procedure given in Prugniel & Soubiran 2001 paper.
Each file has 3 extensions (HDU):
The first (INTENSITY) gives the flux distribution calibrated in
"instrumental" flux, that roughly
corresponds to the flux measured on the detector (it is corrected for
blaze and diffuse light effects). The region of some telluric absorption or of some gliches were masked
and replaced by
IEEE undefined values (be aware that some old FITS readers may not
handle them intelligently
and that you may have to replace them by regular values, (for example
The second extension (FCA_NOR) is a flux calibration relation which can
be used by Pleinpot to
convert the spectrum into flux normalized to the pseudo-continuum. This
was used during the processing and may not be ideally suited for
astrophysical use of the spectrum,
like comparison with synthetic spectra to determine abundances. It is
advised to determine a more relevant continuum using the spectrum in instrumental flux. It is of course possible
to use the processing pipeline in the customize menu of the Elodie
archive to get the standard continuum normalized spectrum.
The third extension (NOISE) is the noise associated to each value in the
The s2D FITS file (s2d button) consists in two extensions (HDU, Header Data Unit):
The first extension contains the
extracted and deblazed spectrum as a 2 dimensional image. Each line of
1024 pixels corresponds to an order, from the
bluest to the reddest. There are 67 orders. On each line the wavelength
grows from the first pixel
to the last and the relation between pixels and wavelength is given by a
series of keywords
(Tchebicheff polynomials) described in the ELODIE manual. For more details read the Elodie documentation.
The Pleinpot routine, img_wca_elodie,
may be used to get the wavelength of each pixel.
The s2d spectrum is corrected for the curvature of the échelle orders, but due to a bad correction of the scattered light residual curvature can still remain. Such a correction is made in the wavelength resampled spectrum.
The second extension, a 2D image 1024x67, is the function used to
correct the extracted spectrum from the blaze.
Multiplying it with the first extension will restitute the extracted
spectrum scaled in detected electrons. This form is useful in particular to determine the noise attached to each pixel.