Observational calibration of the projection factor of Cepheids I. The type II Cepheid κ  Pavonis

• Published in: Astronomy and astrophysics (Berlin) Vol. 576; p. A64
• Main Authors: Breitfelder, J, Kervella, P, Merand, A, Gallenne, A, Szabados, L, Anderson, R I, Willson, M, Le Bouquin, J-B
• Format: Journal Article
• Language: English
• Published: EDP Sciences 01.04.2015
• Subjects: Astronomy; Astrophysics; Calibration; Cepheid variables; Estimates; Parallax; Physics; Projection; Pulsation; Stars
• ISSN: 0004-6361; 1432-0746; 1432-0756
• DOI: 10.1051/0004-6361/201425171

The distance of pulsating stars, in particular Cepheids, are commonly measured using the parallax of pulsation technique. The different versions of this technique combine measurements of the linear diameter variation and the angular diameter variation amplitudes, to retrieve the distance in a quasi-geometrical way. The value of the p-factor and its possible dependence on the pulsation period are still widely debated. Our goal is to measure an observational value of the p-factor of the type-II Cepheid Kappa Pavonis. The parallax of the type-II Cepheid Kappa Pav was measured with an accuracy of 5% using HST/FGS. We used this parallax as a starting point to derive the p-factor of Kappa Pav, using the SPIPS technique (Spectro-Photo-Interferometry of Pulsating Stars), which is a robust version of the parallax-of-pulsation method that employs radial velocity, interferometric and photometric data. Individual estimates of the p-factor are fundamental to calibrating the parallax of pulsation distances of Cepheids. Together with previous observational estimates, the projection factor we obtain points to a weak dependence of the p-factor on period.