Volume 438, Number 1, July IV 2005
|Page(s)||L9 - L12|
|Published online||06 July 2005|
Letter to the Editor
The projection factor of δ Cephei
A calibration of the Baade-Wesselink method using the CHARA Array
LESIA, UMR8109, Observatoire de Paris-Meudon, 5, place Jules Janssen, 92195 Meudon Cedex, France e-mail: email@example.com
2 National Optical Astronomical Observatory 950 North Cherry Avenue, Tucson, AZ 85719, USA
3 Center for High Angular Resolution Astronomy, Georgia State University, PO Box 3965, Atlanta, Georgia 30302-3965, USA
Accepted: 7 June 2005
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, δ Cep. The value we determined, ± 0.06, confirms the generally adopted value of within 1.5 sigmas. Our value is in line with recent theoretical predictions of Nardetto et al. (2004, A&A, 428, 131).
Key words: techniques: interferometric / stars: variables: Cepheids / stars: individual: δ Cep / cosmology: distance scale
© ESO, 2005
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.