ISO. Monitoring the mass loss of a very late Helium flash star

Abstract

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 that in the period from February 1997 to February 1998 the flux over the whole wavelength range has increased by a factor of about ten. Combined with ground-based data we conclude that this increase is the result of mass loss from Sakurai's object and the formation of hot dust around it. Using a spherically symmetric dust radiative transfer model we obtain a quantitative result 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 retracing its own evolutionary history as a consequence of a very late Helium flash. We conclusively demonstrate that significant mass loss is associated with such an event and foster the link to the other few known examples of final Helium flashes. ISO is an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands and the United Kingdom) and with the participation of ISAS and NASA.} observations of dust formation in Sakurai's object