SIMBAD references

2013MNRAS.430..459D - Mon. Not. R. Astron. Soc., 430, 459-471 (2013/March-3)

The horizontal branch in the UV colour-magnitude diagrams - II. The case of M3, M13 and M79.


Abstract (from CDS):

We present a detailed comparison between far-ultraviolet (UV)/optical colour-magnitude diagrams obtained with high-resolution Hubble Space Telescope data and suitable theoretical models for three Galactic globular clusters: M3, M13 and M79.

These systems represents a `classical' example of clusters in the intermediate-metallicity regime that, even sharing similar metal content and age, show remarkably different horizontal branch morphologies. As a consequence, the observed differences in the colour distributions of horizontal branch stars cannot be interpreted in terms of either first (metallicity) or a second parameter such as age.

We investigate here the possible role of variations of initial helium abundance (Y). Thanks to the use of a proper setup of far-UV filters, we are able to put strong constraints on the maximum Y (Ymax) values compatible with the data. We find differences ΔY_max∼0.020.04 between the clusters with M13 showing the largest value (Ymax ∼ 0.30) and M3 the smallest (Ymax ∼ 0.27). In general, we observe that these values are correlated with the colour extensions of their horizontal branches and with the range of the observed NaO anticorrelations.

Abstract Copyright: © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society (2013)

Journal keyword(s): stars: evolution - stars: horizontal branch - globular clusters: individual: M3 - globular clusters: individual: M13 - globular clusters: individual: M79 - ultraviolet: stars

Simbad objects: 15

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