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Friday, June 30, 2006
Tuesday, June 13, 2006
VLT Image of a Unique Swarm of Stars, 47 Tuc
[link :: 47 Tuc]
The Southern constellation Tucana (the Toucan) is probably best known as the home of the Small Magellanic Cloud, one of the satellite galaxies of the Milky Way. But Tucana also hosts another famous object that shines thousands of lights, like a magnificent, oversized diamond in the sky: the globular cluster 47 Tucanae. More popularly known as 47 Tuc, it is surpassed in size and brightness by only one other globular cluster, Omega Centauri....
http://www.eso.org/outreach/press-rel/pr-2006/pr-20-06.html
Thursday, June 08, 2006
Abundance anomalies in hot HB stars of NGC 2808
[Paper]
Pace, G.; Recio-Blanco, A.; Piotto, G.; Momany, Y.
Abundance anomalies in hot horizontal branch stars of the Galactic globular cluster NGC 2808
Astronomy and Astrophysics, Volume 452, Issue 2, June III 2006, pp.493-501
Aims.We present metallicity measurements of 25 stars in the blue horizontal branch of the Galactic globular cluster NGC 2808.
Methods: . Our measurements are based on moderate-resolution spectra taken with the multi-object fiber facility FLAMES-UVES, mounted on Kueyen at the Very Large Telescope.
Results: . We confirm that stars hotter than a threshold temperature have super-solar abundance, while the cooler ones respect the nominal metallicity of the cluster, i.e. [Fe/H]≃-1.1. The threshold temperature is estimated to be about 12 000 K, corresponding to the so called u-jump, and coincides with the sudden departure of the cluster horizontal branch from the models. The metallicity increases with temperature for star hotter than the jump, confirming the hypothesis that the process responsible for this abrupt metallic enhancement is the levitation due to the strong radiation field in absence of a significative convective envelope. A metallicity dependence of the abundance enhancement is also suggested, with more metal poor clusters having a higher increase in metal content.
Conclusions: .The slope in the temperature vs. abundance diagram is higher than the errors involved, and the metal content of the cluster plays possibly a role in determining the amplitude of the jump (more metal poor clusters show more enhancement after the jump), although other parameters, such as clusters' characteristics and even the atomic species involved, may also someway contribute.
ADS Link
Pace, G.; Recio-Blanco, A.; Piotto, G.; Momany, Y.
Abundance anomalies in hot horizontal branch stars of the Galactic globular cluster NGC 2808
Astronomy and Astrophysics, Volume 452, Issue 2, June III 2006, pp.493-501
Aims.We present metallicity measurements of 25 stars in the blue horizontal branch of the Galactic globular cluster NGC 2808.
Methods: . Our measurements are based on moderate-resolution spectra taken with the multi-object fiber facility FLAMES-UVES, mounted on Kueyen at the Very Large Telescope.
Results: . We confirm that stars hotter than a threshold temperature have super-solar abundance, while the cooler ones respect the nominal metallicity of the cluster, i.e. [Fe/H]≃-1.1. The threshold temperature is estimated to be about 12 000 K, corresponding to the so called u-jump, and coincides with the sudden departure of the cluster horizontal branch from the models. The metallicity increases with temperature for star hotter than the jump, confirming the hypothesis that the process responsible for this abrupt metallic enhancement is the levitation due to the strong radiation field in absence of a significative convective envelope. A metallicity dependence of the abundance enhancement is also suggested, with more metal poor clusters having a higher increase in metal content.
Conclusions: .The slope in the temperature vs. abundance diagram is higher than the errors involved, and the metal content of the cluster plays possibly a role in determining the amplitude of the jump (more metal poor clusters show more enhancement after the jump), although other parameters, such as clusters' characteristics and even the atomic species involved, may also someway contribute.
ADS Link
Preprints: W. Miller, F. Schweizer
Preprints:
Globular Clusters in Dwarf Galaxies
Author: Bryan W. Miller (Gemini Observatory)
Recent work on globular cluster systems in dwarf galaxies outside the Local Group is reviewed. Recent large imaging surveys with the Hubble Space Telescope and follow-up spectroscopy with 8-m class telescopes now allow us to compare the properties of massive star clusters in a wide range of galaxy types and environments. This body of work provides important constraints for theories of galaxy and star cluster formation and evolution.
http://arxiv.org/abs/astro-ph/0606062
Globular Cluster Formation in Mergers
Author: Francois Schweizer (Carnegie Observatories, Pasadena)
Mergers of gas-rich galaxies lead to gravitationally driven increases in gas pressure that can trigger intense bursts of star and cluster formation. Although star formation itself is clustered, most newborn stellar aggregates are unbound associations and disperse. Gravitationally bound star clusters that survive for at least 10-20 internal crossing times (~20-40 Myr) are relatively rare and seem to contain <10% of all stars formed in the starbursts. The most massive young globular clusters formed in present-day mergers exceed omega Cen by an order of magnitude in mass, yet appear to have normal stellar initial mass functions. (...)
http://arxiv.org/abs/astro-ph/0606036
Globular Clusters in Dwarf Galaxies
Author: Bryan W. Miller (Gemini Observatory)
Recent work on globular cluster systems in dwarf galaxies outside the Local Group is reviewed. Recent large imaging surveys with the Hubble Space Telescope and follow-up spectroscopy with 8-m class telescopes now allow us to compare the properties of massive star clusters in a wide range of galaxy types and environments. This body of work provides important constraints for theories of galaxy and star cluster formation and evolution.
http://arxiv.org/abs/astro-ph/0606062
Globular Cluster Formation in Mergers
Author: Francois Schweizer (Carnegie Observatories, Pasadena)
Mergers of gas-rich galaxies lead to gravitationally driven increases in gas pressure that can trigger intense bursts of star and cluster formation. Although star formation itself is clustered, most newborn stellar aggregates are unbound associations and disperse. Gravitationally bound star clusters that survive for at least 10-20 internal crossing times (~20-40 Myr) are relatively rare and seem to contain <10% of all stars formed in the starbursts. The most massive young globular clusters formed in present-day mergers exceed omega Cen by an order of magnitude in mass, yet appear to have normal stellar initial mass functions. (...)
http://arxiv.org/abs/astro-ph/0606036
Monday, June 05, 2006
Dedication...
Just a line, to let you know that the "Globular Clustes Database" from now on, is dedicated to my father, Vittorio Castellani, who passed away on May 20, 2006.
He told me several times to keep on on this project, so... daddy, these pages are for you: from where you are now, please from time to time, take a look and see if I'm doing a "good job" ... ;)
Marco Castellani
He told me several times to keep on on this project, so... daddy, these pages are for you: from where you are now, please from time to time, take a look and see if I'm doing a "good job" ... ;)
Marco Castellani
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