Notes on disentangling of spectra II. Intrinsic line-profile variability due to Cepheid pulsations

TL;DR

This paper evaluates the Fourier-disentangling technique for measuring pulsation velocities in Cepheid stars, demonstrating its dependence on line formation depth and potential for improving distance measurements.

Contribution

It introduces modifications to the KOREL-code for fitting pulsation-related line-profile broadening and applies it to Cepheid spectra, advancing spectral disentangling methods.

Findings

Velocity and line-strength variation depend on line formation depth.

Disentangling pulsations can aid in more accurate distance determination.

Pulsation velocities vary with excitation potential.

Abstract

The determination of pulsation velocities from observed spectra of Cepheids is needed for the Baade-Wesselink calibration of these primary distance markers. The applicability of the Fourier-disentangling technique for the determination of pulsation velocities of Cepheids and other pulsating stars is studied. 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 delta Cep in the H-alpha region observed with the Ondrejov 2-m telescope. 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. The disentangling of pulsations in the Cepheid spectra may be used for distance determination.