Only one in two million stars in our galactic environment is of type O, a category that includes stars with anywhere between sixteen and more than one hundred solar masses, and luminosities millions of times greater than that of the sun. Such stars end their lives in supernovae and have a decisive influence on the structure and evolution of galaxies. They are responsible, among others, for the existence of some of the elements we are composed of, but their scarcity makes them difficult to study. The GOSSS catalogue, which has just published data concerning 448 objects, constitutes a window to these stellar giants.
Stars are classified in types O, B, A, F, G, K and M (where the first are the most massive and hottest) depending on the lines of their spectra. These lines are obtained by passing the light emitted by stars through a prism, and they correspond to the different chemical elements that compose them. If the data are corrupted, however, or if different observation techniques are used, classification errors can occur. For example, in some catalogues theta1 Orionis A appears as type O, when it actually is a type B star. This is not an isolated case.
“GOSSS (Galactic O-Star Spectroscopic Survey) substantially improves on prior catalogues,” says Alfredo Sota, researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) in charge of publishing the data. “It is a very ambitious project from the point of view of the number of objects and the quality of the data; it will yield a homogeneous sample, with data from both hemispheres which will be constantly updated, so it will be a very solid tool,” he concludes.
The spectrum of a celestial object reveals some of its essential characteristics such as distance, age, luminosity or even rate of loss of mass — precious information in the case of O-stars whose origin and evolution still await a comprehensive theory. The GOSSS catalogue, which will cover a total of one thousand O-stars (about 2% of the total of the Milky Way), will allow us to answer key questions about these evasive objects.
Reference: A. Sota, J. Maíz Apellániz, N. I. Morrell, R. H. Barbá, N. R. Walborn, R. C. Gamen, J. I. Arias, E. J. Alfaro. THE GALACTIC O-STAR SPECTROSCOPIC SURVEY (GOSSS). II. BRIGHT SOUTHERN STARS. The Astrophysical Journal Supplement Series, 2014; 211 (1): 10 DOI: 10.1088/0067-0049/211/1/10