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Galactic Archaeology has recently been challenged by the fact that stars observed now in a certain location are not necessarily born there, but could have been kicked out from their birth places by different internal and/or external processes. We have made one of the first attempts to quantify how important stellar mixing could be in the case of our Galaxy, and how much of the original chemodynamical correlations would have been destroyed by such processes. Our unique approach has allowed us to conclude that although stellar mixing does take place in our Galaxy, many of the main relations between chemistry and age suggested by pure chemical evolution models are still generally valid. However, stringent constraints can be obtained only when stellar ages will be known for a large number of field stars. This is certainly one of the goals of Gaia, but in the meantime it has been shown that Asteroseismology can also provide a way to estimate ages of giants, even at large distances from the Sun. Here we present the first results obtained with a sample of CoRoT stars that have APOGEE spectra, in the framework of the CoRoGEE collaboration. The results coming from this still very recent approach (he. asteroseismology of Galactic populations) reveals that we might be on the right track in terms of quantifying radial mixing, but these results also suggest the chemical enrichment of the Galactic disk(s) to have been more complex than previously envisaged. Intriguingly, we find that the use of [a/Fe]-ratios as proxy for age, although generally valid, breaks down for some stars. [ABSTRACT FROM AUTHOR]

The article presents the Sun as the benchmark for stellar structure and evolution theory where a validation of its theoretical model is crucial for an accurate description of the internal structure and evolution of other stars. It cites a new solar metallicity where oxygen contributes to 43% showing that the Sun is in agreement with surrounding insterstellar medium and nearby B-stars. It notes the use of 3D models as a step towards a more realistic description of the solar photospheric layers.

The article discusses ways to determine the abundance of oxygen in different regions of the Universe by first presenting different scales and notation used for said purpose. It notes that each field of astronomy has its own metrics like abundance, when applied to an element like oxygen, usually refers to the ratio of its number density to that of hydrogen. It cites the use of a scale in cool star atmospheres as abundances are determined in relation to reference value and not in absolute value.

The article discusses the overall building of oxygen in galaxies over the ages as part of the aspect in the chemical evolution of galaxies. It defines chemical evolution as a study of the transformation of gas stars and the resulting evolution of the chemical composition of a galaxy. This galaxy for chemical evolution process offers a useful framework where one can interpret the body of observational data on elemental and isotopic abundances in stars of various ages.

In this chapter, we first introduce the nuclear processes by which oxygen isotopes can be synthesised and destroyed. We then describe the main astrophysical sites where these reactions may occur, with special emphasis on massive stars and low/intermediate mass stars. [ABSTRACT FROM AUTHOR]

A foreword to "Oxygen in the Universe," is presented.