Sakurai's Object : a rapidly evolving star

Abstract

Sakurai's Object provides an exciting opportunity to study stellar evolution in real time. This rapidly evolving star discovered in early 1996 by Yukio Sakurai has been observed throughout 1997, and photometric observations are available for 1996. During this period it decreased in temperature from 7800K to 5200K, and increased in luminosity by a factor of 4. The temperature became low enough for a significant amount of carbon containing molecules to form and the star's spectral type changed from a G supergiant to a C-R3 supergiant. The change in temperature and luminosity is consistent with the object expanding from 40R⊙ to 200R⊙. The temperature and-luminosity calculated for a distance of 8kpc locate Sakurai's Object at the coolest extent of the final flash evolutionary track for a 0.6 M⊙ planetary nebula nucleus. At the end of the 1997 observing season Sakurai's Object was still increasing in luminosity. It is expected that eventually this increase will cease and the object will evolve at constant luminosity back to higher temperatures