Why some red giant atmospheres have more carbon than oxygen

For the first time, scientists analyze the chemical compositions of cold red giant atmospheres

What is the composition of certain R type stars? Where does all the carbon in their shell come from? These are the questions that guide the research work carried out by scientists from the Department of Theoretical Physics and Cosmos Research at the University of Granada in Spain. In their work, the scientists performed an analysis of the chemical components and the evolution of the spectral states of R-type carbon stars in order to try to explain the source of the abundance of carbon found in their atmospheres.

So far, almost no chemical composition analyzes have been conducted for this type of star. Certain R-type stars are strange red giants, since their mantles have higher levels of carbon than oxygen (the normal composition in the universe is just the opposite). They are classified under the category of 'hot R stars' or 'cold R stars', depending on their temperature.

In the case of cold R stars, the present study constitutes the first analysis of the chemical properties conducted in the world, and for hot R stars, their chemical analyzes already existed.

The research was conducted by Olga Zamora Sánchez and appointed professors Carlos Abia and Inmaculada Dominguez. The scientists used theoretical as well as observational information.

This study found the chemical compositions of R stars, with the help of spectra in the high-resolution optical fields, with the aim of investigating the origin of these stars.

The scientists concluded that cold R stars are the same as N stars (ordinary carbon stars) that are in the AGB (asymptotic giant branch) phase, while hot R stars are different. About 40% of hot R stars have been misclassified so far, so their proportion of red giants may be smaller than previously estimated.

The study constitutes the most comprehensive analysis in the observational and theoretical field of spectral R stars, done worldwide. In addition, the scientists performed for the first time a numerical simulation that simulates the formation of an R star: fusion that makes a white dwarf with the help of red giant helium. And finally, the formation of an R star of the requested type did not occur, but this is also a great contribution, because it means that there are many more challenges and unexplored models.

The scientists say that although the immediate application of their conclusions cannot be seen, it contributes to future studies in the field of cosmology and the question of our formation, because carbon is an important component in the formation and development of life in the universe.

The researchers' press release