Issue EAS Publications Series Volume 6, 2003 Observing with the VLTI Page(s) 253 DOI 10.1051/eas:2003023

Observing with the VLTI
G. Perrin and F. Malbet (eds)
EAS Publications Series, Vol. 6, 2003
DOI: 10.1051/eas:2003023

VLTI/MIDI observations of the circumstellar shell of an AGB star: W Hydrae

R. de Grijs¹, M. Marengo² and G. Pietrzynski<sup>3

1</sup>  Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
²  Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
³  Universidad de Concepción, Departamento de Física, Casilla 160-C, Concepción, Chile; Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warsaw, Poland

Abstract
W Hydrae is a prototype AGB star with a dusty circumstellar shell. The shell is marginally resolved at ground-based sub-arcsecond resolution; the unresolved dust condensation radius is expected to be of order 30-50 mas. Since the dusty circumstellar shell is brightest in the mid-IR, the high spatial resolution required at mid-infrared wavelengths can currently only be achieved by using MIDI on the VLTI. We therefore outline a possible observing programme for the VLTI, using MIDI at 10  m. In a single night of short-baseline VLTI observations with two Auxiliary Telescopes, we can achieve sufficient  (u,v) plane coverage to resolve the shell geometry of W Hya, which will provide strong constraints on the mass loss processes in late-type stars. We expect to either obtain an estimate of the dust condensation temperature, or evidence for interrupted mass loss.

© EAS, EDP Sciences 2003

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