Distances and Absolute Ages of Galactic Globular Clusters from Hipparcos Parallaxes of Local Subdwarfs

TL;DR

Using Hipparcos parallaxes and spectroscopic data, this study refines distances and ages of globular clusters, indicating they are younger than previously thought and consistent with standard cosmological models.

Contribution

The paper provides new distance and age estimates for globular clusters based on Hipparcos data, revealing a shorter distance scale and younger ages than ground-based measurements.

Findings

Hipparcos parallaxes are smaller than ground-based ones.

Globular cluster ages are approximately 2.8 Gyr younger than previous estimates.

The derived cluster ages are around 11.8 Gyr, compatible with inflationary universe models.

Abstract

High precision trigonometric parallaxes from the HIPPARCOS satellite and accurate metal abundances ([Fe/H], [O/Fe], and [alpha/Fe]) from high resolution spectroscopy for about 30 local subdwarfs have been used to derive distances and ages for a carefully selected sample of nine globular clusters. We find that HIPPARCOS parallaxes are smaller than the corresponding ground-based measurements leading, to a longer distance scale (~ 0.2 mag) and to ages ~ 2.8 Gyr younger. The relation between the zero age horizontal branch (ZAHB) absolute magnitude and metallicity for the nine programme clusters is : Mv(ZAHB) = (0.22 +/- 0.09)([Fe/H]+1.5) + (0.48 +/- 0.04) The corresponding Large Magellanic Cloud distance modulus is (m-M)o=18.61 +/- 0.07. The age of the bona fide old globular clusters (Oosterhoff II and Blue Horizontal Branch) based on the absolute magnitude of the turn-off is: Age = 11.8 (+2.1/-2.5) Gyr The present age of globular clusters does no longer conflict with standard inflationary models for the Universe.