Stars live for a long life but most massive stars have lived for millions of years. Towards the end of massive stars, they usually go through the yellow supergiant phase. The phase is usually short hence making the stars rare. Astronomers from Lowell Observatory were able to identify hundreds of these rare yellow massive stars together with the red super giants in two adjacent galaxies. The research helped Lowell astronomers provide strict observation test for their theoretical models that showed how the stars changed from blue, to yellow and finally to red. The constraints help in theoretical predictions and in explaining how certain stars explode as supernovae. Red super giants comprise of Antares, Mu Cephei and Betelgeuse while yellow super giants include Rho Cassiopeiae and Canopus.
Lowell Observatory Astronomers used Multiple Mirror Telescope in Arizona and NOAO facilities in Chile to observe the red and yellow massive stars in galaxies of Large Magellanic Cloud (LMC) and M33 that were nearest. Their observations and theoretical results matched those from Geneva Observatory’s computer models in Switzerland. Astronomers believe that Hertz sprung-Russell diagram helps in understanding the evolution of a star and its lifetime. The stars appear bright and have temperatures; this is because they are fueled by hydrogen in their core. However, the temperature and brightness of these stars do change once the star’s core wears out at the end of the stellar life. Mathematical models that depend on Hertz sprung-Russell diagram are used to predict how the temperature and the brightness of a star changes over its life span.
Previously, evolution models predicted many yellow super giants that lived longer than the real stars. The Lowell group studied supergiants in the nearby galaxies but not in our Milky Way because the latter brought challenges in identifying and characterizing the stars and their diverse distances. The astronomers selected starts according to the angular motion and colors across the sky and then used Hydra, and Chile’s spectrograph on the Blanco 4-meter telescope to obtain spectra for approximately 2,000 stars for the LMC study .The same spectra was obtained after using Arizona’s Hectospec on the 6.5-meter MMT telescope. The spectra present the radio velocity of the star.