Hipparcos Parallaxes and Proper Motions of Cepheids and their Implications

TL;DR

This paper uses Hipparcos data to refine Cepheid distance measurements, confirming their role in the extragalactic distance scale, galactic rotation, and age estimates of globular clusters, leading to improved cosmic distance and age calibrations.

Contribution

It provides the first direct zero-point calibration of Cepheid period-luminosity relations from parallaxes, refining the extragalactic distance scale and galactic parameters.

Findings

Cepheid-based distance scale increased by 8-10%

Galactic rotation constants derived from proper motions

Age of metal-poor globular clusters estimated at about 11 Gyr

Abstract

A summary is given of an analysis of the Hipparcos trigonometrical parallaxes and proper motions of classical Cepheids. It is possible for the first time to derive zero-points for the period-luminosity and period-luminosity-colour relations from parallaxes alone, avoiding the problems of less direct methods. The results imply an increase of 8 to 10 percent in the extragalactic distance scale based on Cepheids. The proper motions are used to derive the constants of galactic rotation. Comparison with radial velocity data leads to a confirmation of the Cepheid distance scale derived from the parallaxes and indicates a kinematic distance to the galactic centre of 8.5 +/- 0.5 kpc. From the new Cepheid distances to the LMC and M31, the absolute magnitude of RR Lyrae variables in metal-poor globular clusters is derived. Applying this to data on metal-poor clusters in our own Galaxy leads to an age of about 11 Gyr for these clusters, considerably less than previously thought. Other evidence from Hipparcos on these matters is briefly reviewed and it is suggested that the Cepheid results currently provide the most reliable scale on which to base distances and ages.