The age of globular clusters

Abstract

I review here recent developments which have affected our understanding of both the absolute age of globular clusters and the uncertainties in this age estimate, and comment on the implications for cosmological models. This present estimate is in agreement with the range long advocated by David Schramm. The major uncertainty in determining ages of globular clusers based upon the absolute magnitude of the main sequence turn-off remains the uncertainty in the distance to these clusters. Estimates of these distances have recently been upwardly revised due to Hipparcos parallax measurements, if one calibrates luminosities of main sequence stars. However, it is important to realize that at the present time, different distance measures are in disagreement. A recent estimate is that the oldest clusters are 11.5 ± 1.3 Gyr, implying a one-sided 95% confidence level lower limit of 9.5 Gyr, if statistical parallax distance measures are not incorporated. Incorporating more recent measures, including Hipparcos based statistical parallax measures, raises the mean predicted age to 12.8 ± 1 Gyr, with a 95 % confidence range of 10-17 Gyr. I conclude by discussing possible improvements which may allow a more precise age distribution in the near future.

Space, Time, and Matter: Cosmological Parameters 2001

“…Others have carried out independent, but similar studies, and at the present time, rough agreement has been obtained between the different groups (i.e. see 13 ). I will not belabor the detailed history of all such efforts here.…”

A Determination of the Hubble Constant from Cepheid Distances and a Model of the Local Peculiar Velocity Field

“…measured from the turno † point in the Hertzsprung-Russell diagrams of old globular clusters. The best current estimates (Krauss 2000 ; see also Caretta et al 2000) suggest that Gyr (1 p error), and that t * \ 12.8^1.0 10 ¹ t * ¹ 17 Gyr at 95% conÐdence. If one furthermore assumes that the globular clusters did not form until about *t D 1 Gyr after the big bang, then the age of the universe as indicated by the oldest stars is Gyr.…”

Local constraints on the oscillatingGmodel

“…In fact, in this case the constraint (5) is automatically satisfied (β = 0), whereas the constraints (2) and (4), together with the "plateau hypothesis" [8] that ensures a successful nucleosynthesis, fix the values of the remaining parameters φ 0 (∼ 10 −3 ) and ξ (∼ 6). The evolution of the model with these conditions result in a value for the age of the Universe compatible with the standard bounds [16].…”