The projection factor of delta Cephei A calibration of the Baade-Wesselink method using the CHARA Array

Mérand Antoine; Pierre Kervella; Vincent Coude Du Foresto; Stephen T. Ridgway; Jason P. Aufdenberg; Theo A. Ten Brummelaar; David H. Berger; Judit Sturmann; Laszlo Sturmann; Nils H. Turner; Harold A. Mcalister

arXiv · astro-ph/0506695

The projection factor of delta Cephei A calibration of the Baade-Wesselink method using the CHARA Array

Mérand Antoine·Pierre Kervella·Vincent Coude Du Foresto·Stephen T. Ridgway·Jason P. Aufdenberg·Theo A. Ten Brummelaar·David H. Berger·Judit Sturmann·Laszlo Sturmann·Nils H. Turner·Harold A. Mcalister

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Abstract

Cepheids play a key role in astronomy as standard candles for measuring intergalactic distances. Their distance is usually inferred from the Period-Luminosity relationship, calibrated using the semi-empirical Baade-Wesselink method. Using this method, the distance is known to a multiplicative factor, called the projection factor. Presently, this factor is computed using numerical models - it has hitherto never been measured directly. Based on our new interferometric measurements obtained with the CHARA Array and the already published parallax, we present a geometrical measurement of the projection factor of a Cepheid, delta Cep. The value we determined, p = 1.27$\pm$0.06, confirms the generally adopted value of p = 1.36 within 1.5 sigmas. Our value is in line with recent theoretical predictions of Nardetto et al. (2004).

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Mérand Antoine, Pierre Kervella, Vincent Coude Du Foresto, Stephen T. Ridgway, Jason P. Aufdenberg, Theo A. Ten Brummelaar, David H. Berger, Judit Sturmann, Laszlo Sturmann, Nils H. Turner, Harold A. Mcalister. 2005-06-28. The projection factor of delta Cephei A calibration of the Baade-Wesselink method using the CHARA Array. https://arxiv.org/abs/astro-ph/0506695

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