Evolution of stars

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. 

Planetary nebulae (PNe) offer the opportunities 1) to study stellar nucleosynthesis in the advanced phases of stellar evolution of stars in the wide mass range - -O. S to Mq and 2) to probe radial and as well horizontal/vertical chemical gradients in spiral galaxies by the time of formation of their progenitors. 

The hottest stars have absorption features in the photosphere associated with lighter elements, some in highly ionised states, but the lower temperature stars have a more diverse atomic composition the coolest stars show molecular emission spectra. This suggests an evolution of stars that involves the formation of heavier elements and ultimately molecules. 

The four general types of stars (main sequence, white dwarfs, giants and supergiants) provide a classification based on the fundamental observable properties but also suggest an evolution of stars. Astrochemically, the cooler giants and supergiants have many more atomic and molecular species that are the products of the nuclear fusion processes responsible for powering the stars. The nuclear fusion processes allow for the formation of more of the elements in the Periodic Table, especially the heavier elements that dominate life on Earth - principally carbon. 

M. Salaris and S. Cassisi, Evolution of Stars and Stellar Populations, John Wiley, Chichester, 2005. 

An excellent review of the s-process is given in the article by F. Kappeler, H. Beer and K. Wisshak, Rep. Prog. Phys., 52, 945 (1989), while the evolution of stars through the AGB stage, with consequences for the s-process, is comprehensively reviewed by... 

Baade, W. 1963, The Evolution of Stars and Galaxies, Cambridge, Mass. Harvard University Press reprinted by Cambridge, Mass. MIT Press 1975. 

The distribution of elements in the cosmos is the result of many processes, and it provides a powerful tool to study the Big Bang, the density of baryonic matter, nucleosynthesis and the formation and evolution of stars and galaxies. This textbook, by a pioneer of the field, provides a lucid and wide-ranging introduction to the interdisciplinary subject of galactic chemical evolution for advanced undergraduates and graduate students. It is also an authoritative overview for researchers and professional scientists. 

H. Kohn, Numerical integration of the Fokker-Planck equation and the evolution of stars clusters, Astrophys. J 234, 1036 (1979). 

Physics is also concerned with the very large think about cosmology and astrophysics. Issues include the beginning of the universe, known as the Big Bang, which occurred some 13.7 billion years ago, the expansion of the universe, formation and evolution of stars and galaxies, and properties of black holes. Here too there are connections between physics and chemistry the origin of the atoms in nuclear reactions within stars and the nature of molecules found in interstellar space, for example. 

In a classic article published in the journal Review of Modern Physics in 1957, Burbidge, Burbidge, Fowler and Hoyle described the various processes responsible for synthesising chemical elements during the evolution of stars. These processes include thermonuclear fusion and neutron capture. 

This chapter concerns the fields that use inorganic mass spectrometry to investigate the composition and evolution of matter in the universe and in the solar system. Cosmochemistry is related to nuclear astrophysics, because almost all the chemical elements were synthesized by nuclear reactions in the interior of stars.1 Mass spectrometric analyses of elemental composition, the distribution and variation of isotope abundances are very helpful, especially for cosmochronological studies, in order to explain the formation, history and evolution of stars in our universe and to understand the chemical and nuclear processes. 

Zeldovich Ya. B., Novikov I. D. Teoriia tiagotenila i evoliutsiia zvezd [Theory of Attraction and Evolution of Stars]. Moscow Nauka, 484 p. (1971). 

Black dwarfs Cooled-off white dwarfs. The final stage in the evolution of stars of roughly one solar mass. Black dwarfs are not massive enough to permit nuclear reactions. 

Figure 9.3 Tuning of cosmic expansion. Some researchers feel that the expansion of the Universe is tuned to permit the evolution of stars and life. If the universe expands too fast, no galaxies or stars form.

Carbon is the fourth most abundant element in the universe. Its abundance in the Sun is about one-half that of oxygen, butreveals differing ratios to oxygen in other stars and in nebulae. The most abundant isotope of carbon, 12C, is the fourth most abundant nucleus in the universe. The two most abundant, 2H and 4He, are remnants of the Big Bang, whereas l60, the third most abundant, and 12C are created during the evolution of stars. Carbon ranks therefore as one of the great successes of stellar nucleosynthesis. The evolution of stars makes evident why this is so. From the isotopic decomposition of normal carbon one finds that the mass-12 isotope, 12C, is 98.9% of all C isotopes. 

Oxygen is the third most abundant element in the universe. Its most abundant isotope, l60, is the third most abundant isotope in the universe. The most abundant two, 1H and 4He, are remnants of the Big Bang, whereas oxygen is created during the evolution of stars. In that sense l60 is the greatest success of stellar nucleosynthesis. 

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. 

Lambert D. L. (1991) The abundance connection—the view from the trenches. In Evolution of Stars The Photospheric Abundance Connection (eds. G. Michaud and A. Tutukov). Kluwer, Dordrecht, pp. 451 —460. 

Being connected to the evolution of stars, SN studies overlap with practically all fields of the modern astronomy, from physics of tiny interstellar medium (e.g. [90]) to the formation of superdense neutron stars [82], As was also pioneered by Baade and Zwicky, they are sources of astrophysical shocks in which cosmic ray particles are accelerated [17]. 

In conclusion, we have shown how nebulae can provide powerful tools to investigate the evolution of stars and to probe the chemical evolution of galaxies. Nevertheless, is necessary to keep in mind the uncertainties and biases involved in the process of nebular abundance derivation. These are not always easy to make out, especially for the non specialist. One of the aims of this review was to help in maintaining a critical eye on the numerous and outstanding achievements of nebular Astronomy. 

Stellar spectroscopy has been a very valuable tool for studying the composition and evolution of stars in our Galaxy. Recent improvements in instrumentation and the construction of 8-10m telescopes has allowed this kind of work to be extended to other galaxies. It is not possible yet to do routine spectroscopy of F and G main sequence stars outside the Milky Way, so these studies have concentrated on A and B type supergiants or red giants. Nevertheless, detailed abundance studies of individual stars is not likely to extend far beyond the Local Group for some time because of telescope size limitations. 

The distribution of elements in the cosmos is the result of many different physical processes in the history of the Universe, from Big Bang to present times. Its study provides us with a powerful tool for understanding the physical conditions of the primordial cosmos, the physics of nucleosynthesis processes that occur in different objects and places, and the formation and evolution of stars and galaxies. Cosmochemistry is a fundamental topic for many different branches of Astrophysics as Cosmology, Stellar Structure and Evolution, Interstellar Medium, and Galaxy Formation and Evolution. 

The evolution of stars is a complex process, hut a simplified overview of the process is as follows ... 

Following main-sequence burning, the ultimate evolution of stars more massive than ss 8M is quite different. Initial evolution is similar, the star expands... 

The parameter which defines the evolution of a star more than any other is mass. Clearly (Sect. 4), the more massive a star, the more luminous and the more quickly it evolves. There is not enough space here to discuss the individual evolution of stars up and down the main-sequence and at different metallicities. However there are some important classifications to make. 

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