Direct diameter measurements of Cepheid variables are used to calibrate the Barnes-Evans Cepheid surface brightness relation.
More than 50 separate Cepheid diameter measurements from four different optical interferometers are used to calculate surface brightnesses as a function of magnitude and color. For two Cepheids, η Aquilae and ζ Geminorum, high precision diameter measurements as a function of pulsation phase are available from the Palomar Testbed Interferometer (PTI). Relations using only these diameters are found for each individual Cepheid in order to search for differences between Cepheids of different pulsation period. In all cases the best-fit relations are simple linear relations between surface brightness and color with the constraint that for a spectral type A0 star (where all colors equal zero) all relations must yield the same surface brightness (i.e., there must be a common zero-point). The derived relations found using interferometric Cepheid diameters are consistent with functions in the literature found using
interferometric observations of non-variable giant and supergiant stars. In addition, while the separate relations for η Aquilae and ζ Geminorum are marginally consistent within the errors they do differ in the direction predicted for Cepheids of differing pulsation period. Using these new surface brightness relations the
distance is calculated to the nearby Cepheid δ Cephei for which
a new distance has been found using trigonometric parallax with
the Hubble Space Telescope. These distances are well within the
errors of the distance derived from trigonometric parallax.
We examine our measured Cepheid diameters and the uncertainties as estimated from observations of calibrators and check stars, using (delta) Cephei, for which we have the most data, as our example. The mean limb-darkened diameter of (delta) Cep is 1.520 +/- 0.014 mas. The pulsation is only weakly seen, if at all, a tantalizing result that however does not determine the distance with useful precision. The longer baselines currently under construction will provide both high-precision diameters and a post-facto check of our uncertainty estimates.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.