The Horizontal Branch in the UV Colour Magnitude Diagrams. II. The case of M3, M13 and M79

Дата и время публикации : 2012-12-18T16:40:33Z

Авторы публикации и институты :
Emanuele Dalessandro
Maurizio Salaris
Francesco R. Ferraro
Alessio Mucciarelli
Santi Cassisi

Ссылка на журнал-издание: Ссылка на журнал-издание не найдена
Коментарии к cтатье: Accepted for publication by MNRAS. 15 pages, 15 figures, 1 table
Первичная категория: astro-ph.SR

Все категории : astro-ph.SR, astro-ph.GA

Краткий обзор статьи: We present a detailed comparison between far-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 (Y_{max}) values compatible with the data. We find differences Delta Y_{max} ~ 0.02-0.04 between the clusters with M13 showing the largest value (Y_{max} ~ 0.30) and M3 the smallest (Y_{max} ~ 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 Na-O anti-correlations.

Category: Physics