Free Astronomy Magazine July-August 2014

JULY-AUGUST 2014 STELLAR EVOLUTION radial velocity differs by about 50 km/s from the average of the cluster. The researchers ruled out a random superposition of Wd1- 5 with the cluster, and analysis of the com- position of its atmosphere showed odd abundances of surface elements, incom- patible with the mass, luminosity and evo- lutionary stage of the star. In particular, a disproportionate enrichment of carbon (and to a lesser extent helium and nitro- gen) has been measured, which is unexplain- able if we assume that Wd1-5 has evolved since its birth as a single star. The excess carbon in its atmosphere is equal to 0.05 solar masses, and a similar amount cannot have risen from the inside, but it must have been accreted from an external source. In proposing that thousands of years ago Wd1-5 formed a binary system with J1647- 45, Clark and colleagues exemplify its broad evolution as follows. It all starts with two blue stars of about 41 and 35 solar masses (respectively the future Wd1-5 and the future J1647-45), orbiting around a common centre of gravity with a period of just 8 days. At one point, in the core of the more massive of the two, the primary fuel, hydrogen, starts to run out, and one of the consequences is the moderate expansion of its outer layers, with the star that begins to transform into a giant blue. The close proximity of the smaller compan- ion does though cause this latter to start capturing an ever rising amount of the atmo- T he Kueyen telescope (8.2 metres diameter), one of four ne- arly-identical units that make up the Very Large Telescope of the ESO. With this in- strument some European astro- physicists have shown how and why magnetars originate. [ESO]