Free Astronomy Magazine September-October 2014

STELLAR EVOLUTION red supergiants present in our galaxy and in nearby gal- axies. In recent years, howe- ver, more sophisticated math- ematical models and new observations have made it possible to greatly improve the understanding of red supergiants, permitting re- searchers to start from more solid bases and thus conduct more targeted studies. The most interesting result in this direction was produced by a work just recently con- cluded by Emily Levesque, Philip Massey, Anna Ż ytkow (that one) and Nidia Mor- rell. The team, using the in- struments of the Apache Point Observatory (New Mexico) and of the Las Cam- panas Observatory (Chile), analyzed the spectra of about sixty red supergiants belonging to the Milky Way and the Magellanic Clouds. One of those, a star called HV 2112 located in the Small Magellanic Cloud, has proven K ip Thorne (third from left) photographed at the École de Physique des Houches few years before proposing the T Ż O model with Anna Ż ytkow. ratio between the abundances of these chemical elements and those of some more “traditional” elements, such as nickel, iron, calcium and potassium. Despite these pro- mising theoretical ba- ses, any past attempt to distinguish a classic red supergiant from a T Ż O has been ineffec- tive, either because it was impossible to si- multaneously measure the abundances of mul- tiple elements, or be- cause possible excesses detected could be ex- plained by resorting to nucleosynthesis process- es already known, or al- so for the not accurate characterization of the A synthetic scheme of the inner work- ings of Thorne- Ż ytkow objects. The small cross in- dicates the posi- tion of the neu- tron star, while the central light area is the region where the iso- topes characteriz- ing the T Ż O atmo- spheres are pro- duced. The outer area shows how the motions of the convective gaseous envelope transport these isotopes to the surface, and at the same time supply the nucleus with new hydro- gen to burn. [Dig- ital Sky Survey/ Centre de Don- nées astronomi- ques de Strasbourg]