Virginia Trimble, professor of physics at the University of California, Irvine, and visiting professor of astronomy at the University of Maryland, has said recently:

 

We don't often see stars change their spectral types in a human lifetime. Thus, FG Sagittae, which brightened, cooled from about BO to K, and added lines of carbon, barium, and other elements to its spectrum in the century after 1890 was long seemingly unique. The standard interpretation has been that it experienced its very last flash of helium shell burning (the products are carbon and oxygen) and was about to become an R Coronea Borealis variable. These are carbon-rich stars that fade suddenly and unpredictably (which FG Sge started doing a couple of years ago) and that have hydrogen-depleted atmospheres (which FG Sge has just developed). In addition, the "galloping giant" is no longer alone. Examination of old images and spectrograms reveal that V 605 Aquilae, studied by Knut Lundmark in the 1920's was a similar sort of beast, though it is now very faint. And the latest recruit is V 4334 Sagittarii, better known as Sakurai's object, for its 1994 discoverer. It, too, changed both spectral type and surface composition very rapidly, and is now hydrogen-poor and carbon-rich, and well on its way to becoming the century's third new R CrB star.