An article accepted for publication in the journal “Astronomy & Astrophisics” describes a study on the star V766 Cent, also known as the HR 5171 A, the largest yellow hypergiant discovered so far. A team of researchers used ESO’s Very Large Telescope Interferometer (VLTI) to conduct new observations and compare them to the previous ones. The observation of the evolution of V766 Cent is made more complicated by the fact that a companion passes in front of it.
The V766 Centauri system, also known as HR 5171 and with other names, was cataloged as a binary in 1927. Approximately 12,000 light years away from Earth, it’s been studied with various instruments until in 1971 the star V766 Cent was identified as a yellow hypergiant. This is a very rare type of star and in this case a really huge one with a diameter about 1,400 times the Sun’s.
Subsequent studies brought new data but a recent one also questioned its classification. After all, the V766 Cent could be a red supergiant that is rapidly losing mass and is in the transition phase that is turning it into a yellow hypergiant. In recent years, VLTI has been used more than once to observe V766 Cent with a companion, a smaller star that could still be a supergiant, very close to it.
The picture shows V766 Cent with its companion in three different periods: in the first one its companion is passing behind it while in the second and third period it’s passing in front of it. This makes this study even more interesting but also complex so the estimate of the two stars’ masses is quite difficult. V766 Cent has a mass estimated between 27 and 36 solar masses while its companion’s is between 2 and 20 solar masses.
For the latest observations, the VLTI was used in the configuration including the four auxiliary telescopes and the PIONIER (Precision Integrated-Optics Near-infrared Imaging ExpeRiment) instrument. This allows to get many details about that pair of stars but their closeness makes the astronomers’ task still difficult. Surely there will be more studies on V766 Cent, a really rare object, and its companion to better understand an unusual stage in the life cycle of some stars.