Notes on disentangling of spectra

Abstract

Context. The determination of pulsation velocities from observed spectra of Cepheids is needed for the Baade-Wesselink calibration of these primary distance markers.Aims. The applicability of the Fourier-disentangling technique for the determination of pulsation velocities of Cepheids and other pulsating stars is studied.Methods. The KOREL-code was modified to enable fitting of free parameters of a prescribed line-profile broadening function corresponding to the radial pulsations of the stellar atmosphere. It was applied to spectra of Cep in the H-alpha region observed with the Ondřejov 2-m telescope.Results. The telluric lines were removed using template-constrained disentangling, phase-locked variations of line-strengths were measured and the curves of pulsational velocities obtained for several spectral lines. It is shown that the amplitude and phase of the velocities and line-strength variations depend on the depth of line formation and the excitation potential.Conclusions. The disentangling of pulsations in the Cepheid spectra may be used for distance determination. © 2009 ESO.