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Astron. Astrophys. 352, 619-622 (1999)

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2. Observations

Exploratory observations of GD 229 were made in 1994 with the UBVRI polarimeter (Piirola, 1973, 1988) attached to the 1.25 m telescope of the Crimean Astrophysical Observatory. These measurements revealed the difference in the magnitude of both circular and linear polarization and position angle in comparison with the data published in the past (Berdyugin, 1995). In November 1996 and 1997, we made new high S/N observations of GD 229 and G 240-72 using a similar polarimeter (Korhonen et al., 1984) at the 2.5 m Nordic Optical Telescope (NOT), La Palma. Both linear and circular polarization have been measured for GD 229 with superachromatic [FORMULA] plate as the polarization modulator, and only linear polarization for G 240-72 ([FORMULA] plate). The instrumental polarization was determined by observations of standard non-polarized stars. It was found to be of [FORMULA] 0.05% in all passbands and, therefore, negligible for our study. In order to transform the observed polarization from the instrumental to the standard coordinate system, the highly polarized standard HD 204827 was observed. The scale and sign of the circular polarization was checked by observations of Grw+70o8247.

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© European Southern Observatory (ESO) 1999

Online publication: December 2, 1999