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Astron. Astrophys. 326, 218-220 (1997)

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2. Observation

From December 2 through 6, 1994 phaseresolved flux and circular polarization spectra were simultaneously taken at the Cassegrain focus of the 3.5m telescope of the German Spanish Astronomical Center with the "TWIN"-spectrograph and additionally implemented triple diaphragm and quarter wave plate. In this telescope configuration three double spectra are produced, one double spectrum for the object and two for simultaneous measurements of the sky background. The circular polarization spectrum is then calculated by the difference between the corresponding single spectra divided by their sum. The sum of the corresponding single spectra yields the flux spectrum. Intrinsic polarization of the optics was checked for by observing several early type SAO stars, which were assumed to be circularly unpolarized. All spectra were then correspondingly corrected. The grisms were selected such that the spectra cover the spectral ranges between 3700-5500 Å (blue channel) and 5700-7300 Å (red channel), respectively.

Since we were not interested in absolute fluxes, a flux standard (Feige 34) was observed only once during the observing run, in order to get the right continuum slopes.

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© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998