Astronomy and Astrophysics – Astrophysics – Solar and Stellar Astrophysics
Scientific paper
2010-06-10
Astronomy and Astrophysics
Astrophysics
Solar and Stellar Astrophysics
Accepted for publication in the MNRAS on 2010 June 8. Received 2010 May 19; in original form 2010 February 9. 7 pages and 3 fi
Scientific paper
Spectroscopy has shown the presence of the CN band dicothomy and the Na-O anticorrelations for 50--70% of the investigated samples in the cluster 47 Tuc, otherwise considered a "normal" prototype of high metallicity clusters from the photometric analysis. Very recently, the re-analysis of a large number of archival HST data of the cluster core has been able to put into evidence the presence of structures in the Sub Giant Branch: it has a brighter component with a spread in magnitude by $\sim$0.06 mag and a second one, made of about 10% of stars, a little fainter (by $\sim$0.05 mag). These data also show that the Main Sequence of the cluster has an intrinsic spread in color which, if interpreted as due to a small spread in helium abundance, suggests $\Delta$Y$\sim$0.027. In this work we examine in detail whether the Horizontal Branch morphology and the Sub Giant structure provide further independent indications that a real --although very small-helium spread is present in the cluster. We re--analyze the HST archival data for the Horizontal Branch of 47 Tuc, obtaining a sample of $\sim$500 stars with very small photometric errors, and build population synthesis based on new models to show that its particular morphology can be better explained by taking into account a spread in helium abundance of 2% in mass. The same variation in helium is able to explain the spread in luminosity of the Sub Giant Branch, while a small part of the second generation is characterized by a small C+N+O increase and provides an explanation for the fainter Sub Giant Branch. We conclude that three photometric features concur to form the paradigm that a small but real helium spread is present in a cluster that has no spectacular evidence for multiple populations like those shown by other massive clusters.
Antona F. D'
Di Criscienzo Marcella
Milone André
Piotto Giampaolo
Ventura Paolo
No associations
LandOfFree
The helium spread in the Globular cluster 47 Tuc does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The helium spread in the Globular cluster 47 Tuc, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The helium spread in the Globular cluster 47 Tuc will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-492264