2023-06-29 14:15:45
The stars are the fundamental bricks that constitute the galaxies and, therefore, the observable universe. Within the different types of stars, there are some with more than 8 times the mass of the Sun, called massive stars, whose intense radiation and strong stellar winds have a great impact on the environment that surrounds them. Inside it, atoms heavier than hydrogen and helium are forged and are crucial for the chemical evolution of galaxies and, ultimately, for the appearance of life. In addition, after their death as supernovae, they give rise to the so-called neutron stars and black holes. All this makes understanding its nature and evolution of great importance.
In this context, those massive stars that are in an intermediate stage of their lives are called blue supergiants, a crucial moment, similar to a stellar “adolescence”, which will forever determine the rest of their lives and their final destiny. Due to the complexity of this evolutionary phase, previous investigations, based on samples with a few tens of these stars, have not been able to provide enough information to know them in detail.
In a new study, observations of some 750 blue supergiant stars up to 6,500 light-years from Earth have been obtained, making them one of the highest quality and most complete samples ever made. For this study, the IACOB project of the Instituto de Astrofísica de Canarias (IAC) in Spain has spent more than 15 years obtaining very high-quality, high-resolution spectra (the “fingerprints” of stars) of massive stars, also developing a exhaustive search for blue supergiants in the Milky Way to be able to examine the vast majority of them. These observations have been made mainly with the NOT and Mercator telescopes, located at the Roque de los Muchachos Observatory, in La Palma, one of the Canary Islands.
Image of an area of our cosmic neighborhood, in the constellation Perseus, with the blue supergiant stars in the study marked with crosses and including a characteristic spectrum of the sample. (Images: Abel de Burgos Sierra (IAC). CC BY-SA)
“The analysis of this sample allows us to address some of the questions about the evolutionary nature and physical properties of these objects that have not been resolved for decades, since they are not as well known as other types of less massive stars, despite the fact that they have a great importance in many fields of modern astrophysics”, explains Abel de Burgos Sierra, co-author of the study, a researcher at the University of La Laguna on the Canary Island of Tenerife and a researcher at the IAC.
For the selection of the sample, a new filtering method based on an easily identifiable trace in the spectra of these stars (the shape of the H-beta line) has been used. Through a simple measurement, this new methodology allows a quick and effective identification of stars with a specific surface temperature and gravity. In this way, the researchers have not needed to infer these data from the usual techniques of spectroscopic analysis using complex models of stellar atmospheres.
“This will be crucial to identify stars of this type when the next large spectroscopic surveys of massive stars such as WEAVE-SCIP from Roque de los Muchachos, or 4MIDABLE-LR from La Silla, in Chile, begin to observe thousands of stars in our galaxy. every night for the next five years”, comments Sergio Simón-Díaz, IAC researcher, co-author of the study and Principal Investigator of the IACOB project, an international collaboration led by the IAC whose objective is to create the basis of spectra of massive stars of the Milky Way largest of all built.
The next step, which De Burgos is already working on as part of his doctoral thesis, is to obtain precise data on physical parameters (masses, temperatures, luminosities) and chemical abundances (He, C, N, O, Si) for the sample of 750 blue supergiants. “This will help answer some of the most interesting questions that remain unanswered and that will allow us to better understand this ‘adolescent’ phase of massive stars,” concludes Miguel A. Urbaneja, a researcher at the University of Innsbruck in Austria and co-author of the study.
The study is titled “The IACOB project. IX. Building a modern empirical database of Galactic O9 – B9 supergiants: sample selection, description, and completeness”. And it has been published in the academic journal Astronomy and Astrophysics. (Source: IAC)
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