Red giant star

Red giant stars, both in the field and in globular clusters, present abundance anomalies that can not be explained by standard stellar evolution models. Some of these peculiarities, such as the decline of 12C/13C, and that of Li and 12C surface abundances for stars more luminous than the bump, clearly point towards the existence of extra-mixing processes at play inside the stars, the nature of which remains unclear. Rotation has often been invoked as a possible source for mixing inside Red Giant Branch (RGB) stars ([8], [1], [2]). In this framework, we present the first fully consistent computations of rotating low mass and low metallicity stars from the Zero Age Main Sequence (ZAMS) to the upper RGB. 

Abstract. We present preliminary results of 3D hydrodynamical simulations of surface convection in red giants stars. We investigate the main differences between static ID and 3D time-dependent model stellar atmospheres of red giants for a range of metallicities between solar and [Fe/H] = —3 focusing in particular on the impact of 3D spectral line formation on the derivation of stellar abundances. 

Boothroyd Sackmann (1999). Thus, to solve the 3He problem in terms of extra-mixing in low-mass stars, the vast majority of them (90%-100%) must be affected by this phenomenon (Galli et al. 1997). The same conclusion has been reached independently by Charbonnel do Nascimento (1998) on the basis of the statistics of carbon isotopic ratios in a sample of red-giant stars with accurate Hipparcos parallaxes. 

Much information on the theoretical and observational aspects of AGB evolution can be found in H. R. Johnson and B. Zuckerman (cds.), Evolution of Peculiar Red Giant Stars, Cambridge University Press 1989. 

The main s process synthesises neufron-rich nuclei with atomic number A greater than 100 and occurs in asymptotic giant branch (AGB)-type red giant stars undergoing thermal palpitations. 

Red giant stars, which are coolar than the sun, produce energy by means of the reaction jBe + H 5Li+5He+ eneiigy... 

Oxygen isotopic compositions of presolar oxide grains compared with those of red giant stars. Stellar data are shown without error bars, which are large on this scale. Both data sets are characterized by higher 170/160 ratios and lower 180/160 ratios compared to solar oxygen. Stellar data from Smith and Lambert (1990). 

II. Difficulties of Mass-Loss Mechanisms in Red Giant Stars... 

Also, one classical question is whether dust formation initiates mass-loss or whether dust is formed as a result of mass-loss. It is to be noted that the latter process may be rather easy, once mass-loss occurs by another mechanism. This problem can be examined on the basis of recent observations of CO radio emission lines, by which stellar mass-loss rate has been determined with better accuracy than by any other method for a large sample of red giant stars, and terminal flow velocities have also been determined with high accuracy( e.g.,Knapp,Morris,1985). The result revealed that the momentum in the stellar wind and that in the stellar radiation do not necessarily show good correlation(e.g.,Zuckerman,Dyck,1986). Also, a necessary condition for the winds to be accelerated by radiation pressure on dust( Mv [Pg.160]

Mira variables form an important subgroup of the red giant stars which are typical representatives of stars showing burnt material at their surfaces. Since the photospheres of Miras are not in hydrostatic equilibrium but are characterized by spherically very extended density stratifications, their properties and emitted spectra differ substantially from those of non-Miras, and any attempts to analyse Mira spectra by means of conventional techniques must fail. Non-hydrostatic models are needed for analysis work. 

The rate of mass loss is proportional to T (Duncan et al. 1986). Thus, an analogue of HR diagram with neutrino luminosity versus neutrino effective temperature is desirable to represent numerical results. If we assume the structure of polytrope with N=3 and take account of the definition of the neutrino sphere, we can calculate a neutrino Hayashi-line analogously to that for red giant stars. We have shown that numerical results could be understandable if analyzed with appropriate concepts. 

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