M. A. Hendry

A new method for estimating the distance of young open clusters

We present a new technique for estimating the distance to young open clusters. The method requires accurate measurement of the axial rotation period of late-type members of the cluster: rotation periods are first combined with projected rotation velocities and an estimate of the angular diameter for each star - obtained using the Barnes-Evans relation between colour and surface brightness. A best cluster distance estimate is then determined using standard techniques from the theory of order statistics, which are in common use in the general statistics literature. It is hoped that this new method will prove a useful adjoint to more traditional distance methods, and will provide a better determination of the distance scale within the solar neighbourhood

The age of the universe

Abstract Astronomers have two approaches to trying to determine the age of the Universe. They can estimate the ages of individual objects in the Universe and specifically in our Galaxy. These estimates use either the observed properties of stars and theoretical ideas concerning stellar evolution or the abundances of long-lived radioactive isotopes and their decay products. Alternatively they can use cosmological theories and observations to try to determine the age of the entire Universe. Obviously the Universe must be older than its component parts but neither of the above methods is sufficiently reliable that this is true of the deduced ages. As a result, it is from time to time reported that some object in the Universe is older than the Universe itself. In this article we discuss the methods that are currently being used to determine the age and we emphasize the problems in obtaining reliable results. It is not at present possible to provide a definite value for the age of the Universe.

THRESHOLDS ON STAR FORMATION AND THE CHEMICAL EVOLUTION OF GALACTIC DISCS : COSMOCHRONOLOGY AND THE AGE OF THE GALAXY

In this paper we analyse different chronometers based on the models of chemical evolution developed in Chamcham, Pitts \& Tayler (1993; hereafter CPT) and Chamcham \& Tayler (1994; hereafter CT). In those papers we discussed the ability of our models to reproduce the observed G-dwarf distribution in the solar neighbourhood, age-metallicity relation and radial chemical abundance gradients. We now examine their response to the predictions of cosmochronology. We use the recent production ratios of the actinide pairs

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New distance measurements to the Pleiades and

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Persei clusters

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Optimal galaxy distance estimators

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A deep search for radio emission from three X-ray pulsars : are radio emission and X-ray pulsations anticorrelated ?

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Bias in Velocity Field Recoveries

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