1,721,016 research outputs found
The effect of mass loss on the chemical yields from massive stars
No full textRecent results on the calculation of the chemical yields from massive stars are rediscussed by taking into account the occurrence of mass loss by stellar wind during the core H(-) and He-burning phases. The new yields are found to be compatible with the observed distribution of chemical abundances in the solar system, except for He. The net enrichment of several elements over the Galaxy's lifetime is found to be consistent with the current estimate of the star formation rate, if a two phase process of galaxy formation (halo-disk) is adopted. The relative He to heavy element enrichment rate turns out to agree with the observational value when mass loss by stellar wind is taken into account
Galactic orbits of the old open clusters NGC 188, NGC 2682, NGC 2420, NGC 752 and NGC 2506
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The Galactic system of old open clusters: age calibration and age-metallicity relation
Full text linkEvolution and nucleosynthesis of primordial very massive stars
No full textWe present evolutionary models of zero-metallicity (Pop-III) very massive objects (VMOs) , with initial masses in the range 120 Msun - 1000 Msun. In the attempt of exploring the possible occurrence of mass loss by stellar winds, calculations are carried out with suitable formalisms for the mass-loss rates driven by radiation pressure and stellar rotation. The corresponding wind chemical yields are presented. Finally, with the aid of a simple chemical model, the primordial helium and metal enrichments, and the resulting Delta Y/Delta Z ratio are discussed
The red tail of carbon stars in Local Group galaxies systems
No full textC-stars separate well from O-rich giants in near-infrared colours, drawing a striking red tail in recent colour-magnitude diagrams for Local Group galaxies. Most present-day stellar models are unable to account for this feature. However, it is naturally reproduced when AGB models are computed with consistent variable molecular opacities
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