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Subject: Astrophysics ×

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Now showing 1 - 3 of 3
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    Nucleosynthesis in the first massive stars
    (Bristol : IOP Publ., 2018) Choplin, Arthur; Meynet, Georges; Maeder, André; Hirschi, Raphael; Chiappini, Cristina
    The nucleosynthesis in the first massive stars may be constrained by observing the surface composition of long-lived very iron-poor stars born around 10 billion years ago from material enriched by their ejecta. Many interesting clues on physical processes having occurred in the first stars can be obtained based on nuclear aspects. First, in these first massive stars, mixing must have occurred between the H-burning and the He-burning zone during their nuclear lifetimes; Second, only the outer layers of these massive stars have enriched the material from which the very iron-poor stars, observed today in the halo of the MilkyWay, have formed. These two basic requirements can be obtained by rotating stellar models at very low metallicity. In the present paper, we discuss the arguments supporting this view and illustrate the sensitivity of the results concerning the [Mg/Al] ratio on the rate of the reaction 23Na(p,γ)24Mg.
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    A multiwavelength study of the Stingray Nebula; properties of the nebula, central star, and dust
    (Bristol : IOP Publ., 2016) Otsuka, Masaaki; Parthasarathy, Mudumba; Tajitsu, Akito; Hubrig, Swetlana
    We performed a detail chemical abundance analysis and photo-ionization modeling of the Stingray Nebula (Hen3-1357, Parthasarathy et al. 1993[1]) to more characterize this PN. We calculated nine elemental abundances using collisionally excited lines (CELs) and recombination lines (RLs). The RL C/O ratio indicates that this PN is O-rich, which is supported by the detection of the broad amorphous silicate features at 9 and 18 μm By photo-ionization modeling, we investigated properties of the central star and derived the gas and dust masses. The nebular elemental abundances, the core-mass of the central star, and the gas mass are in agreement with the AGB model for the initially 1.5 M⊙ stars with the Z = 0.008.
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    The dynamical evolution of planetary nebulae
    (Bristol : IOP Publ., 2016) Schönberner, Detlef
    Based on modern 1D-radiation-hydrodynamics simulations of formation and evolution of planetary nebulae, I discuss in detail the basic dynamical processes responsible for the "grand design" of most planetary nebulae, i.e. their double-shell morphology and their typical expansion properties. Special emphasis is given for a proper definition of a nebula's true expansion rate and its relation to spectroscopically measurable Doppler velocities of the expanding material. It is found that the typical nebular expansion is about twice as fast as hitherto assumed, viz. ≃45 kms-1.