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A&A Supplements series, Vol. 123, May II 1997, 173-177

Received March 13; accepted September 16, 1996

An attempt to detect polarization effects in the envelope of tex2html_wrap_inline1044 Cassiopeiae with the GI2T interferometer

K. Rousselet-Perrauttex2html_wrap1078 - F. Vakilitex2html_wrap1080 - D. Mourardtex2html_wrap1082 - F.  Morandtex2html_wrap1084 - D. Bonneautex2html_wrap1086 - Ph. Steetex2html_wrap1088

Send offprint request: F. Vakili

tex2html_wrap1090  IGRAP, Laboratoire d'Astronomie Spatiale, CNRS, Traverse du Siphon, BP. 8, 13376, Marseille Cedex 12, France
tex2html_wrap1092  Observatoire de la Côte d'Azur, Département Fresnel, CNRS URA 1361, 06460 Saint Vallier de Thiey, France


We report on the results of an observing run of tex2html_wrap_inline1048 Cassiopeiae using the optical long baseline interferometer Grand Interféromètre à 2 Télescopes (GI2T) in the southern France equipped with film-sheet polarizers. Four interferometric baselines ranging from 20 to 40 m were obtained on this star during 1994 on September 5th and 6th, with tex2html_wrap_inline1050 Cephei as a calibrator. We aimed at detecting possible variations of the angular diameter of tex2html_wrap_inline1052 Cas as a function of polarization directions parallel and orthogonal to the north-south baseline of the GI2T. We do not detect any variation of the visibility as a function of Hour Angle on tex2html_wrap_inline1054 Cephei, neither on tex2html_wrap_inline1056 Cas. We find an upper limit of 1.3 on the ratio of the angular diameters of the envelope of tex2html_wrap_inline1058 Cas seen through polarizers parallel and perpendicular to the North-South direction of the GI2T's baseline. We discuss how this limit could constrain density laws in the wind of this Be star. We clearly resolve tex2html_wrap_inline1060 Cas for increasing baselines in the red continuum whatever the polarization. Assuming the continuum flux originating from a photosphere surrounded by an elliptical gaussian envelope we estimate the extent of the latter as (tex2html_wrap_inline1062) mas. This diameter agrees well with the Htex2html_wrap_inline1064 emitting envelope as obtained by other interferometers.

keywords: circumstellar matter -- stars: Be - stars: individual (tex2html_wrap_inline1066 Cas) -- stars: imaging -- techniques: interferometric -- polarization

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