High Precision Measurements of RVs: a Powerful Tool for Tomography of Atmospheres of roAp-stars

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Scientific paper

The method of high-precision RV-measurements is based on usage of absorbing iodine cell placed just before the entrance slit to the spectrograph. It acts like the standard wavelength calibrator, which is affected by the same instrumental configuration as the observed data. It was previously developed and used for search for exoplanets (Butler et al., 1996) and later it was applied to study pulsational RV-variations in roAp-stars (Hatzes & Kuerster, 1992, Mkrtichian et al., 2002, Mkrtichian et al. 2003). But due to the spotty distribution of chemical elements on the surfaces of this type of stars one should be interested in obtaining precise RVs in separate spectral lines. As it was shown in Mkrtichian & Hatzes, 2003 the knowledge of pulsational phase and amplitude in separate spectral features allows one to investigate the 3-d structure of the stellar atmosphere and the observed pulsational modes. The different pulsation modes having different oscillation frequencies are expected to have different location heights for acoustic nodes in atmosphere (Gautchy et al., 1998), what leads to the phase differences between different oscillation frequencies measured on the same spectral lines. This is the unique possibility for tomography of stellar atmospheres. And the precise RV- measurements play a key role in such studies. With this aim the standard procedure of calculation within the frames of the high-precision RV-determination method was slightly modified to obtain better accuracies for RVs calculated in separate spectral lines. The description of the modified method is given and the application to the roAp star HD122970 is shown. The results are discussed.

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