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Numerical cross-correlation results

This page describes the results obtained from numerical cross-correlation of the observed spectrum with a spectral mask containing "holes" for more than 3000 selected metallic lines. Each "hole" is described by two edge wavelengths, fine-tuned for the spectral type and resolution.

Two such files were normally used, R37000F0 and R37000K0, for F0 and K0 spectral types, prepared for a slightly broadened spectral resolving power of 37000. Other (private) masks have been used, in particular one useful for A-type stars (prive4, with only 263 lines) and another for M4-type stars (prive1).

This numerical cross-correlation, an optional and interactive part of the on-line data processing at the telescope, can yield accurate radial velocities, even for low S/N spectra, from a single (or double, in the case of spectroscopic binaries) gaussian fit to the cross-correlation profile. The velocities derived are expressed relative to the barycenter of the Solar System. In addition, the 'sigma' of the gaussian and the depth of the profile are also given. Note that the FWHM of the profile is given by 2.354 times 'sigma'.

When doing a cross-correlation on objects observed with the sky in the second fiber (modes OBJ2), presumably in a moonlit sky, the stellar CCF profile is corrected for the effects of contamination by the sky, as derived from prior cross-correlation on the sky fiber.

Note: A complete re-processing of the entire ELODIE database was planned by Geneva Observatory to correct for small effects in the radial velocities due to changes introduced in the subsequent versions of the extraction and cross-correlation software used at the telescope. This project is presently on hold.

This archive is actively maintained. We thus welcome feedback from the user to help us detect anomalies and improve the website.

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