Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-08-13
Astronomy and Astrophysics
Astrophysics
18 pages, 11 figures, accepted in A&A
Scientific paper
10.1051/0004-6361:20077806
In this paper we present multiband optical and UV Hubble Space Telescope photometry of the two Galactic globular clusters NGC 6388 and NGC 6441. We have obtained the first UV color-magnitude diagrams for NGC 6388 and NGC 6441. These diagrams confirm previous results, obtained in optical bands, about the presence of a sizeable stellar population of extremely hot horizontal branch stars. At least in NGC 6388, we find a clear indication that at the hot end of the horizontal branch the distribution of stars forms a hook-like feature, closely resembling those observed in NGC 2808 and Omega Centauri. We briefly review the theoretical scenarios that have been suggested for interpreting this observational feature. We also investigate the tilted horizontal branch morphology and provide further evidence that supports early suggestions that this feature cannot be interpreted as an effect of differential reddening. We show that a possible solution of the puzzle is to assume that a small fraction - ranging between 10-20% - of the stellar population in the two clusters is strongly helium enriched (Y=0.40 in NGC 6388 and Y=0.35 in NGC 6441). The occurrence of a spread in the He abundance between the canonical value (Y=0.26) and the quoted upper limits can significantly help in explaining the whole morphology of the horizontal branch and the pulsational properties of the variable stars in the target clusters.
Blanco Alejandra Recio
Busso Giorgia
Cassisi Santi
Castellani Marco
Catelan Márcio
No associations
LandOfFree
The Peculiar Horizontal Branch Morphology of the Galactic Globular Clusters NGC 6388 and NGC 6441: new insights from UV observations 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 Peculiar Horizontal Branch Morphology of the Galactic Globular Clusters NGC 6388 and NGC 6441: new insights from UV observations, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Peculiar Horizontal Branch Morphology of the Galactic Globular Clusters NGC 6388 and NGC 6441: new insights from UV observations will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-23760