Evolution of the stars

Nucleogenesis and evolution of stars are strongly correlated. The evolution of the stars comprises different stages and depends mainly on their mass, as already mentioned. In all cases, stars of high density are formed at the end of the evolution. 

In stars of small mass ( 0.1 times the mass of the sun) the energy liberated by gravitational contraction is not sufficient to reach the temperature necessary to start thermonuclear reactions. These stars are directly entering the stage of black dwarfs (black holes). 

Within a time of the order of 1 s a great amount of matter is converted into neutrons and the star collapses into an extraordinarily compact mass of neutrons with a density of the order of 10 gcm. Formation of neutron stars represents the reversal of nucleogenesis. Due to the explosion, the outer layers of the star are ejected into interstellar space. 

Formation and decay of stars are continuous processes in the cosmic time scale. Stars of the first generation are formed as a direct consequence of the big bang, whereas those of the second and of following generations are formed at a later stage by aggregation of matter from the debris of bumed-out stars in the interstellar space. 

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S. Chandrasekar (Chicago) theoretical studies of the physical processes of importance to the structure and evolution of the stars. 

The structure and evolution of the stars were the subject of the second part. Spitzer discussed the Physical Processes in Star Formation, a subject that was further developed by Salpeter with special regard to the birthrate function of the stars. W. A. Fowler and Bierman discussed the evolution toward the main sequence and R. Minkowski discussed the data available concerning the supernovae. 

Tinsley B. (1980) Evolution of the stars and gas in galaxies. Fundament. Cosmic Phys. 5, 287-388. 

M. Schwarzschild, Structure and evolution of the stars, Princeton University Press (1958)... 

Naturally occurring radioisotopes that are formed after the "big bang" in the evolution of the stars and have such long half-lives that they and their daughter products are still present, as well as radionuclides that are being continuously produced by nuclear reactions between cosmic radiation and stable elements. Radionuclides released into the envirorunent due to human activities. 

The study of molecular cloud stability and evolution leads naturally to studies of the physical and chemical evolution of the star formation process. Fundamental to this study of the star formation process is the characterization of the physical conditions in the gas and dust comprising these regions. For the gas, volume density n (cm ), kinetic temperature Tk (K), chemical composition X, turbulent motion Ai (km sec ), and magnetic field strength B (Gauss) are fundamental physical quantities. For the dust, the dust temperature (K), dust volume density... 

The evolution of a. star after it leaves the red-giant phase depends to some extent on its mass. If it is not more than about 1.4 M it may contract appreciably again and then enter an oscillatory phase of its life before becoming a white dwarf (p. 7). When core contraction following helium and carbon depletion raises the temperature above I0 K the y-ray.s in the stellar assembly become sufficiently energetic to promote the (endothermic) reaction Ne(y,a) 0. The a-paiticle released can penetrate the coulomb barrier of other neon nuclei to form " Mg in a strongly exothermic reaction ... 

Self-Test 1.3B A red giant is a late stage in the evolution of a star. The average wavelength maximum at 700. nm shows that a red giant cools as it dies. What is the surface temperature of a red giant ... 

Boyd, G., Dutrow, E., and Tunnessen, W., 2008. The evolution of the ENERGY STAR energy performance indicator for benchmarking industrial plant manufacturing energy use, Journal of Cleaner Production, 16, 709-715. 

The formation of stars in the interiors of dense interstellar clouds affects the chemistry of the immediate environment in a variety of ways depending on many factors such as the stage in the evolution of star formation, the mass of the star or protostar, and the density and temperature of the surrounding material. In general, the dynamics of the material in the vicinity of a newly forming star are complex and show many manifestations. Table 3 contains a list of some of the better studied such manifestations, which tend to have distinctive chemistries. These are discussed individually below. 

Figure 19 Schematic effect of the STAR operator on 2JCH and 3,/CH couplings. The vicinal component of magnetization in the long-range response that is two-bond coupled to a protonated carbon experiences modulation, which serves as a pseudo-evolution for this coupling. In contrast, the vicinal component of magnetization in the long-range response that is three-bond coupled to a protonated carbon does not exhibit a F, skew. Homonuclear modulation during the evolution period f, is still present, as the full experiment is not a constant-time experiment.

The studies of other elements in metal-rich planet-host stars is also giving important information about the chemical evolution of the Galaxy. 

Abstract. In an effort to determine accurate stellar parameters and abundances for a large sample of nearby stars, we have performed the detailed analysis of 350 high-resolution spectra of FGK dwarfs and giants. This sample will be used to investigate behavior of chemical elements and kinematics in the thick and thin disks, in order to better constrain models of chemical and dynamical evolution of the Galaxy. 

C. Sneden, I. I. Ivans, J. P. Fulbright Globular Clusters and Halo Field Stars . In Origin and Evolution of the Elements Volume 4, Carnegie Observatories Astrophysics Series, ed. by A. McWilliam, M. Rauch (Cambridge, 2004)... 

The rotation models predict significant effects on the properties and the evolution of the massive stars. They alter the ratio of red to blue supergiants and hence the nature of SNII progenitors they affect the properties, formation and evolution of Wolf-Rayet stars they result in the enrichment of He and C in the ISM while the abundance of O decreases they produce higher He and a-element yields from SNII via larger He cores. Many of these effects are metallicity dependent. With such far ranging impact, the effects of rotation and mass loss on the evolution of massive stars should be thoroughly understood. 

One of the more challenging things to understand in these multiple-fragment models is the evolution of the present-day surviving thin old disk, particularly since a recent accretion of the thick disk could destroy the thin disk. Further, in these models stars should not form in a thin disk at all until after most of the merging is complete, since otherwise disks have too small a scale-length (Navarro Steinmetz 1997). A solution to both these issues may be that the local old thin disk is also accreted in these models. Here the recent results of many authors (cf... 

AGB stars constitute excellent laboratories to test the theory of stellar evolution and nucleosynthesis. Their particular internal structure allows two important processes to occur in them. First is the so-called 3(,ldredge-up (3DUP), a mixing mechanism in which the convective envelope penetrates the interior of the star after each thermal instability in the He-shell (thermal pulse, TP). The other is the activation of the s-process synthesis from alpha captures on 13C or/and 22Ne nuclei that generate the necessary neutrons which are subsequently captured by iron-peak nuclei. The repeated operation of TPs and the 3DUP episodes enriches the stellar envelope in newly synthesized elements and transforms the star into a carbon star, if the quantity of carbon added into the envelope is sufficient to increase the C/O ratio above unity. In that way, the atmosphere becomes enriched with the ashes of the above nucleosynthesis processes which can then be detected spectroscopically. 

What happens for cooler (i.e. less massive) stars on the red side of the Li dip As we shall see now, the stellar mass or the effective temperature of the dip is a transition point for stellar structure and evolution. First of all it is a transition as far as the rotation history of the stars is concerned. Indeed the physical processes responsible for surface velocity are different, or at least operate with different timescales on each side of the dip. At the age of the Hyades, the stars hotter than the dip still have their initial velocity while cooler stars have been efficiently spun down (Fig. 1). This behavior is linked to the variation of the thickness of the superficial H-He convection zone which gets rapidly deeper as Teff decreases from 7500 to 6000K (e.g. TC98). Below 6600 K, the stars have a sufficiently deep... 

Fig. 2. Evolution of field star surface abundances by [17] and theoretical models imposing extra-mixing below the convective envelope by Denissenkov VandenBerg [12]...

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