![]() ![]() This is the highest amount of ejected material astronomers have ever witnessed in a single stellar eruption. Astronomers discovered molecular absorption bands of titanium-oxide (TiO) formed in the slowly expanding atmosphere, suggesting that they had witnessed the formation of a cool and extended shell which was detached from the star by a shock wave carrying a mass equal to 10% of our Sun or 10,000 times the mass of the Earth. The star suddenly cooled down from 7,000 to 4,000 degrees within a few months. However, what happened with Rho Cassiopeiae during the summer of 2000 went beyond anybody's expectations. The observations were aimed at investigating the processes occurring when yellow hypergiants approach and bounce against the Yellow Evolutionary Void, and the results revealed almost regular variations of temperature within a few hundred degrees. The highly efficient Utrecht Echelle Spectrograph has allowed astronomers to monitor Rho Cassiopeiae in detail from 1993 to 2002. The process of approaching the Void however, has not yet been studied observationally in sufficient detail as these events are very rare. During this process these stars end up in a supernova explosion: their ultimate and violent fate. ![]() Theoretically, they cannot cross the Void unless they have lost sufficient mass. When approaching the Void these stars may show signs of peculiar instability. Yellow hypergiants are peculiar stars because they display an uncommon combination of brightness and temperature, which places them in a so-called Yellow Evolutionary Void. It is believed that these stars are at a very evolved stage of their life and will ultimately explode as supernovae. They are very luminous and have surface temperatures between 3,500 and 7,000 degrees. Yellow hypergiants are rare objects there are only 7 of them known in our Galaxy. In spite of being 10,000 light-years away from the Earth, this star is visible to the naked eye as it is over half a million times more luminous than the Sun. Rho Cassiopeiae is one of the brightest yellow "hypergiant" stars in the Milky Way. ![]() The results of this investigation are to be published in a research paper in The Astrophysical Journal on February 1. Nasmyth focal station of the telescope (right).įull size image available through contactĪn international team of astronomers using the Utrecht Echelle Spectrograph on the William Herschel Telescope has identified the bright star Rho Cassiopeiae as the best candidate to undergo a supernova explosion in the near future. The Utrecht Echelle Spectrograph can be seen at the ![]()
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