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Astron. Astrophys. 350, L27-L30 (1999)


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Letter to the Editor

ISO * observations of dust formation in Sakurai's object

Monitoring the mass loss of a very late Helium flash star

F. Kerber 1,2, J.A.D.L. Blommaert 3, M.A.T. Groenewegen 4, S. Kimeswenger 2, H.U. Käufl 5 and M. Asplund 6

1 Space Telescope European Coordinating Facility, European Southern Observatory, 85748 Garching, Germany
2 Institut für Astronomie der Universität Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria
3 ISO Data Centre, ESA, Villafranca, 28080 Madrid, Spain
4 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, 85748 Garching, Germany
5 European Southern Observatory (ESO), Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
6 Uppsala Astronomical Observatory, Box 515, 75120 Uppsala, Sweden

Received 27 May 1999 / Accepted 2 September 1999

Abstract

We present ISOCAM observations of Sakurai's object (V4334 Sgr) covering the wavelength range of 4 to 15 µm 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[FORMULA]/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.

Key words: stars: AGB and post-AGB – stars: evolution – stars: circumstellar matter – ISM: planetary nebulae: individual: Sakurai's Object (V4334 Sgr)

* 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.

Send offprint requests to: F. Kerber (fkerber@eso.org)

© European Southern Observatory (ESO) 1999

Online publication: October 4, 1999

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