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Discovery of the most primitive star in the Galactic halo

A team of European astronomers, including 9 scientists from GEPI, discovered the most primitive star in the halo of our Galaxy. This 0.8 M object, SDSS J102915+172927, is extremely metal poor. They determined its metallicity to be 20,000 times lower than in the Sun. This result goes against the theoterical models suggesting that low-mass stars cannot form from the primitive interstellar medium.

The team used the spectrographs X-shooter and UVES at ESO’s Very Large Telescope (VLT) to observe this star and derive its chemical composition. The spectral region covering Ca II H and K lines are shown in the image.

More details can be found in the ESO press release.

The paper An extremely primitive star in the Galactic halo (Caffau, Bonifacio, François, Sbordone, Monaco, Spite, Spite, Ludwig, Cayrel, Zaggia, Hammer, Randich, Molaro & Hill) is published in Nature.