Can interfero-polarimetry constrain extended atmospheres' models?

Observatoire de Haute-Provence, F-04870 Saint-Michel l'Observatoire, France

Send offprint request to: K. Rousselet-Perraut

Received: 24 April 1997
Accepted: 9 February 1998

Abstract

Adding a polarimetric mode to a stellar interferometer enables to extend its exploration capacities for extended circumstellar environments in which intrinsic polarization becomes a non negligible observable. A general formalism is developed to map intensities and corresponding visibilities in polarized light for any extended atmosphere. To constrain matter distributions in scattering hot envelopes, an instrumental accuracy of 1% on the visibility is required, which is compatible with the performances of existing instruments. This implies an envelope flux contribution of 10 - 15% and limiting visual magnitudes M_v of 4 in a monospeckle mode and of 8 - 10 in multispeckle modes, which allows to contemplate studying several hot stars by this interfero-polarimetric technique. Finally, a specific instrumentation and an adapted methodology are mandatory: observations at small spatial frequencies () where R^* is the stellar radius), simultaneous recordings of the polarized interferograms and an accurate calibration of the instrumental polarization. This technique can be applied to arrays of few telescopes (such as the Very Large Telescope Interferometer - VLTI) as well as to aperture synthesis arrays. Besides, such a polarimetric equipment must be advocated for the future instruments since it greatly reduces the instrumental bias.