Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004sf2a.conf..311n&link_type=abstract
SF2A-2004: Semaine de l'Astrophysique Francaise, meeting held in Paris, France, June 14-18, 2004. Edited by F. Combes, D. Barret
Astronomy and Astrophysics
Astrophysics
Scientific paper
The distance of galactic cepheids can be derived through the interferometric Baade-Wesselink method. The interferometric measurements lead to angular diameter estimations over the whole pulsation period, while the stellar radius variations can be deduced from the integration of the pulsation velocity. This latter is linked to the observational velocity deduced from line profiles, thanks to the so-called projection factor p. The knowledge of p is currently an important limiting factor of this method of distances determination. Thanks to spectroscopic observations of delta Cep, we have constrained a self-consistent and time-dependent model of this star in order to model its atmosphere dynamical structure and to synthesize the consequent line profiles. Different kinds of radial and pulsation velocities are then derived to study the projection factor. In particular, we compile a suitable average value for the projection factor related to different observational techniques, such as spectrometry, interferometry in wide band or in spectral lines. We show that the impact on the average projection factor and consequently on the final distance deduced from this method is of the order of 6%. We also study the impact of a constant or pulsation phase dependent value for the p-factor on the cepheid distance determination. We conclude on this last point that if the average value of the projection factor is correct, then the impact of the time-dependence is not significant as the error on the final distance is of the order of 0.2%.
Bersier David
Fokin Andrei
Kervella Pierre
Mathias Ph.
Mourard Denis
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