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Astron. Astrophys. 321, 791-802 (1997)


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Spectropolarimetry of symbiotic stars: AG Draconis *

H.M. Schmid 1, 2 and H. Schild 1

1 Institut für Astronomie, ETH-Zentrum, CH-8092 Zürich, Switzerland
2 Mount Stromlo and Siding Spring Observatories, ANU, Weston Creek P.O., ACT 2611, Canberra, Australia

Received 24 July 1996 / Accepted 9 October 1996

Abstract

We present a series of spectropolarimetric observations of the symbiotic system AG Dra and focus on the polarization in the [FORMULA] 6825 and [FORMULA] 7082 lines, which are due to Raman scattering of O VI [FORMULA] 1032,1038 emission. The polarization in the Raman lines is variable and the polarization angle shows periodic changes which are linked to the orbital motion even if the object goes into outburst.

From the rotation in the line polarization angle, we find for the orbit inclination [FORMULA] ([FORMULA]). This implies for a reasonable total mass of the binary system that the hot component's mass lies in the range [FORMULA]. This mass is rather low but not in real conflict with the interpretation that the hot component is a CO white dwarf and that the AG Dra system underwent in the past a Barium star type mass transfer episode.

Our observations cover the 1994 outburst phase. During outburst the O VI radiation increased strongly while the Raman scattered radiation remained practically constant. This decrease in Raman efficiency is probably due to a reduction of available H0 scatterers as a consequence of the enlarged ionization during outburst.

We detect intrinsic continuum polarization which is at least partly locked to the orbital motion and therefore also seems to be induced by a scattering process.

Key words: binaries: symbiotic – circumstellar matter – scattering – polarization – stars: individual: AG Dra

* Based on observations obtained with the William Herschel Telescope of the Royal Greenwich Observatory, La Palma, Canary Islands

Send offprint requests to: H. Schild

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998

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