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Fitting the CCF with a gaussian
Gives the barycentric radial velocity (in km/s) derived from fitting a gaussian to the profile obtained from cross-correlating the extracted s2d spectrum with a numerical mask. Masks exist for F0 and K0 spectral types. Additional masks for A and M stars have been used.
For fast rotators or spotted stars, simple gaussians may not give a good fit.

Gives the sigma of the gaussian fitted to the cross-correlation profile. Note that the FWHM of the profile is given by 2.354 times 'sigma'. The CCF was computed over a velocity interval selected by the user (normal, large, extra-large). The normal step is 1 km/s over a ± 70 km/s interval centered on a value set by the user (between -300 and 300 km/s). The width of the CCF can be used to obtain the rotational velocity of the star, v sin(i), once the instrumental width has been determined by calibration on well-known stars. See Queloz et al. (1998).

Gives the amplitude of the gaussian curve fitted to the cross-correlation profile. This is a good approximation to the depth of the CCF dip. It is expressed as a fraction relative to the CCF continuum. The surface of the CCF profile can also be used to derive a metal abundance. See Santos et al. (2002).

Normalized CCF continuum

Case with two gaussians : For spectroscopic binaries, the interactive analysis procedure in the pipeline allowed the simultaneous fitting of two gaussians. In these cases we also give results for the second component (vfit2, sigfit2, ampfit2).

For more information, read the original ELODIE reduction manual :
Reduction user's manual

See also the section on radial velocities in the ELODIE data products page.

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