Related papers: Observational consequences of the hypothesized hel…
Recent observational studies of $\omega$ Centauri by {\it Hubble Space Telescope} have discovered a double main sequence in the color magnitude diagrams (CMDs) of its stellar populations. The stellar population with the blue main sequence…
To study the possible origin of the huge helium enrichment attributed to the stars on the blue main sequence of Omega Centauri, we make use of a chemical evolution model that has proven able to reproduce other major observed properties of…
Recent observations for the color-magnitude diagrams (CMDs) of the massive globular cluster Omega Centauri have shown that it has a striking double main sequence (MS), with a minority population of bluer and fainter MS well separated from a…
The most massive Galactic globular cluster omega Cen appears to have two, or perhaps more, distinct main sequences. Its bluest main sequence is at the centre of debate because it has been suggested to have an extremely high helium abundance…
The double main sequence identified in the globular cluster Omega Centauri has been interpreted using isochrones to indicate a large variation in the abundance of helium. If true, a helium enhancement carries strong implications for the…
UV observations of some massive globular clusters have revealed a significant population of stars hotter and fainter than the hot end of the horizontal branch (HB), the so-called blue hook stars. This feature might be explained either by…
The origin of a double main-sequence (MS) in omega Centauri is explored. We have shown from theoretical calculations on the stellar evolution that the colors of MS stars are shifted to those of the observed blue MS if the surface layers are…
UV observations of some massive globular clusters uncovered a significant population of very hot stars below the hot end of the horizontal branch (HB), the so-called blue hook stars. This feature might be explained either as results of the…
In this contribution we discuss the origin of the extreme helium-rich stars which inhabit the blue main sequence (bMS) of the Galactic globular cluster Omega Centauri. In a scenario where the cluster is the surviving remnant of a dwarf…
A direct measure of the helium abundances from the near-infrared transition of He I at 1.08 micron is obtained for two nearly identical red giant stars in the globular cluster Omega Centauri. One star exhibits the He I line; the line is…
High spectral resolution and high signal-to-noise ratio optical spectra of red giants in the globular cluster Omega Centauri are analysed for stellar parameters and chemical abundances of 15 elements including helium by either line…
[Abbreviated] We have investigated the color-magnitude diagram of Omega Centauri and find that the blue main sequence (bMS) can be reproduced only by models that have a of helium abundance in the range Y=0.35-$0.40. To explain the faint…
The blue Main Sequence (bMS) of $\omega$ Cen implies a ratio of helium to metal enrichment $\Delta Y/\Delta Z \approx 70$, which is a major enigma. We show that rotating models of low metallicity stars, which account for the anomalous…
As part of a large investigation with Hubble Space Telescope to study the faintest stars within the globular cluster Omega Centauri, in this work we present early results on the multiplicity of its main sequence (MS) stars, based on deep…
We interpret the stellar population of $\omega$ Centauri by means of a population synthesis analysis, following the most recent observational guidelines for input metallicities, helium and [(C+N+O)/Fe] contents. We deal at the same time…
The observed abundance variations in globular cluster red giants indicate that these stars may be mixing helium from the hydrogen shell outward into the envelope, presumably as a result of internal rotation. We have investigated the…
Chemical evolution models are presented for the anomalous globular cluster Omega Centauri. After demonstrating that the chemical features of Omega Cen can not be reproduced in the framework of the closed-box self-enrichment scenario, we…
Using a chemical evolution model we investigate the intriguing suggestion that there are populations of stars in some globular clusters (e.g. NGC 2808, omega Centauri) with enhanced levels of helium (Y from about 0.28 to 0.40) compared to…
The most massive Galactic globular cluster, Omega centauri, appears to have multiple populations. Its bluest main sequence and extended horizontal branch stars are suggested to have the common origin, that is, an extremely high helium…
We herein determine the average integrated mass loss from stars stars belonging to the dominant metal-poor population ([Fe/H] ~ --1.7) of the Galactic globular cluster omega Centauri (NGC 5139) during their red giant and horizontal branch…