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Paper: Signs of Accretion in Stellar Abundance Patterns
Volume: 482, 10th Pacific Rim Conference on Stellar Astrophysics
Page: 3
Authors: Yushchenko, A.; Kang, Y. W.; Doikov, D.; Raikov, A.
Abstract: The chemical composition of stellar atmospheres is one of the most important sources of information about the evolution of the Universe. Usually nuclear processes are accepted to be the dominant mechanism of creation the stellar abundance patterns, but in recent years accretion and other phenomena were recognized as a reason of numerous anomalies of chemical composition. Different types of accretion were investigated in previous decades. The accretion of interstellar gas on the time scale compared with stellar age can significantly change the surface abundance patterns. The atoms of interstellar matter, mainly hydrogen and helium atoms, collide the atoms of stellar atmosphere and, as a result of charge-exchange reaction, steal an electron from them. The effect is significant, if the ionization potential of target atom is close to the ionization potential of hydrogen or helium. Part of ionized atom can escape the star. As a result the underabundance of ions with second ionization potentials close to the ionization potentials of hydrogen and helium is observed. It can be also the effective mechanism of braking the stellar rotation. We present the results of investigations of this effect in different types of single and binary stars. It is shown that charge-exchange reaction are important for understanding the chemical composition of stars with effective temperatures between 7000 K and 10600 K.
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