ISO observations of dust formation in Sakurai's object - Monitoring the mass loss of a very late Helium flash star

We present ISOCAM observations of Sakurai's object (V4334 Sgr) covering the wavelength range of 4 to 15 mu m in seven filters. The photometry shows th at in the period from February 1997 to February 1998 the flux over the whol e wavelength range has increased by a factor of about ten. Combined with gr ound-based data we conclude that this increase is the result of mass loss f rom Sakurai's object and the formation of hot dust around it. Using a spher ically symmetric dust radiative transfer model we obtain a quantitative res ult of a variable and increasing mass loss rate reaching some 10(-7) M./yr, a value not uncommon among stars during the Asymptotic Giant Branch (AGB) evolution. This is in agreement with the notion that Sakurai's object is re tracing its own evolutionary history as a consequence of a very late Helium flash. We conclusively demonstrate that significant mass loss is associate d with such an event and foster the link to the other few known examples of final Helium flashes.