English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The distance to pulsating stars is classically estimated using theparallax-of-pulsation (PoP) method, which combines spectroscopic radialvelocity measurements and angular diameter estimates to derive the distance ofthe star. An important application of this method is the determination ofCepheid distances, in view of the calibration of their distance scale. However,the conversion of radial to pulsational velocities in the PoP method relies ona poorly calibrated parameter, the projection factor (p-factor). We aim tomeasure empirically the value of the p-factors of a homogeneous sample of nineGalactic Cepheids for which trigonometric parallaxes were measured with theHubble Space Telescope Fine Guidance Sensor. We use the SPIPS algorithm, arobust implementation of the PoP method that combines photometry,interferometry, and radial velocity measurements in a global modeling of thepulsation. We obtained new interferometric angular diameters using the PIONIERinstrument at the Very Large Telescope Interferometer, completed by data fromthe literature. Using the known distance as an input, we derive the value ofthe p-factor and study its dependence with the pulsation period. We find thefollowing p-factors: 1.20 $\pm$ 0.12 for RT Aur, 1.48 $\pm$ 0.18 for T Vul,1.14 $\pm$ 0.10 for FF Aql, 1.31 $\pm$ 0.19 for Y Sgr, 1.39 $\pm$ 0.09 for XSgr, 1.35 $\pm$ 0.13 for W Sgr, 1.36 $\pm$ 0.08 for $\beta$ Dor, 1.41 $\pm$0.10 for $\zeta$ Gem, and 1.23 $\pm$ 0.12 for $\ell$ Car. These values areconsistently close to p = 1.324 $\pm$ 0.024. We observe some dispersion aroundthis average value, but the observed distribution is statistically consistentwith a constant value of the p-factor as a function of the pulsation period.The error budget of our determination of the p-factor values is presentlydominated by the uncertainty on the parallax, a limitation that will soon bewaived by Gaia.

Observational calibration of the projection factor of Cepheids. II. Application to nine Cepheids with HST/FGS parallax measurements