Probing the dynamical structure of δ Cephei atmosphere

Details Probing the dynamical structure of δ Cephei atmosphere Probing the dynamical structure of δ Cephei atmosphere

Jul 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006a%26a...454..327n&link_type=abstract

Astronomy and Astrophysics, Volume 454, Issue 1, July IV 2006, pp.327-332

Astronomy and Astrophysics

Astrophysics

9

Techniques: Interferometric, Stars: Atmospheres, Stars: Distances, Stars: Oscillations, Stars: Variables: Cepheids

Scientific paper

Context: .Limb darkening and the projection factor are currently two limiting aspects of the interferometric Baade-Wesselink method of Cepheid distance determination. Aims: .We first quantify the impact of the phase dependence of limb darkening on the derived distance. We then study a new way to probe the dynamical structure of Cepheid's atmosphere through spectro-interferometric observations. Methods: .A hydrodynamical model of δ Cep is used to derive stellar disk intensity distribution in the continuum and in different spectral lines, together with the corresponding wavelength- and phase-dependent visibility curves. Results: .We find that considering a constant limb darkening in the visible leads to a systematic shift of about 0.02 in phase on the angular diameter curve. The derived distance is, however, not affected by this effect. Otherwise, for a spectroscopic resolution of R=12 000 in the visible, we find in the most favourable case (maximum contraction velocity) a signature on the visibility curve of about 7% that is clearly detectable by current spectro-interferometers. Nevertheless, the projection factor has only a 1% (or less) effect on the visibility curve. Conclusions: .The spectro-interferometry provides a new geometric view of Cepheid's atmosphere. However, the combination of different techniques (high resolution spectroscopy, spectro- and differential-interferometry) are now needed to efficiently constrain the physical parameters of Cepheids' atmosphere and, in particular the projection factor.

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