Toward a Universal Period-p-factor Relation

Alexandre Gallenne, Pierre Kervella, Antoine Mérand, Grzegorz Pietrzyński, Wolfgang Gieren and Nicolas Nardetto

The parallax-of-pulsation (PoP) method, best known for its photometric variant as the Baade-Wesselink (BW) method, is the most common way to have independent distance measurements by combining the stellar linear radius with the angular diameter variations. The linear radius is estimated via radial velocities that are converted to pulsation velocities by conventionally choosing a multiplicative factor, called the p-factor. This factor depends on the limb darkening and the dynamical behaviour of the line-forming regions, which is rather difficult to quantify without a detailed modelling of the stellar atmosphere. This parameter is currently the main source of uncertainty in the application of the PoP method, leading to a global uncertainty of about 5−10 % on the distance. Here we present an empirical approach which makes use of the Spectro-Photo-Interferometry of Pulsating Stars (SPIPS) algorithm to derive a period-p-factor relation for Galac- tic (MW) and Magellanic Cloud (MC) Cepheids.

Proceedings of the Polish Astronomical Society, vol. 6, 290-291 (2018)

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