نتایج جستجو برای: stars evolution
تعداد نتایج: 389513 فیلتر نتایج به سال:
An approach is introduced for incorporating the concept of stellar pollution into stellar evolution models. The approach involves enhancing the metal content of the surface layers of stellar models. In addition, the surface layers of stars in the mass range of 0.5 − 2.0M⊙ are mixed to an artificial depth motivated by observations of lithium abundance. The behavior of polluted stellar evolution ...
Neutral fluorine (F i) lines are identified in the optical spectra of cool EHe stars. These are the first identification of F i lines in a star’s spectrum, and provide the first measurement of fluorine abundances in EHe stars. The results show that fluorine is overabundant in EHe stars. The overabundance of fluorine provides evidence for the synthesis of fluorine in these stars, that is discuss...
We have conducted an optical long-term monitoring survey of the majority of dwarf galaxies in the Local Group, with the Isaac Newton Telescope (INT), to identify the long period variable (LPV) stars. LPV stars vary on timescales of months to years, and reach the largest amplitudes of their brightness variations at optical wavelengths, due to the changing temperature. They trace stellar populati...
We have investigated the abundance anomalies of lithium for stars with planets in the temperature range of 5600–5900K reported by Israelian and coworkers, as compared to 20 normal stars at the same temperature and metallicity ranges. Our result indicates a higher probability of lithium depletion for stars with planets in the main–sequence stage. It seems that stellar photospheric abundances of ...
The aim of this paper is to look at the evolution of massive stars in order to determine whether or not the progenitor of V838 Mon may be a massive star. In the first part of this paper, the evolution of massive stars around solar metallicity is described, especially the evolution in the Hertzsprung-Russell (HR) diagram. Then, using the observational constraints, the probable progenitors (and t...
We demonstrate the necessity of using realistic stellar models taken from stellar evolution codes, as opposed to polytropes, for starting models in smoothed particle hydrodynamics calculations of collisions between main sequence stars. Evolved stars have mean molecular weight gradients, which affect their entropy profiles and therefore affect how they react during a collision. The structure of ...
We review the theory of electron-conduction opacity, a fundamental ingredient in the computation of low-mass stellar models; shortcomings and limitations of the existing calculations used in stellar evolution are discussed. We then present new determinations of the electron-conduction opacity in stellar conditions for an arbitrary chemical composition that improve over previous works and, most ...
Rapidly accreting massive protostars undergo a phase of deuterium shell burning during pre-main sequence evolution that causes them to swell to tenths of an AU in radius. During this phase, those with close binary companions will overflow their Roche lobes and begin transferring mass. Since massive stars frequently have companions at distances well under 1 AU, this process may affect the early ...
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