Most of our data are low resolution near IR spectra of symbiotic stars. For the purpose of spectral classification, they have been complemented by a set of comparison standard star spectra. Supplementary spectra in the blue wavelength region are employed for the spectral classification of about ten symbiotic systems, which have cool giants without strong molecular bands in the near IR. The data were collected in the course of several observing runs with various instruments. The following subsections describe these instruments and the spectra obtained. A combined log of our data is given in Table 1.
The largest dataset (targets and spectral standard stars) was acquired in 1992 with the 1.52 m telescope of the European Southern Observatory (ESO) in La Silla, Chile. The telescope was equipped with the Boller & Chivens spectrograph and a 2k Ford Aerospace CCD (ESO #24). With grating #19 a wavelength coverage of approximately Å was achieved with a resolution of Å. An OG570 filter isolated the first spectral order.
With the same telescope, R.E. Schulte-Ladbeck had observed some systems already in 1987. She kindly made these data available to us.
Medium resolution spectra of northern symbiotic systems were taken at the Observatoire de Haute-Provence (OHP) in France. The spectra were obtained during six observing runs in 1988 January, June, August and December, and in 1989 May and August. We used the CARELEC spectrograph attached to the Cassegrain focus of the 1.93 m telescope. A grating with a dispersion of 33 Å/mm and a RCA CCD were used, giving a resolution of 1 Å/pixel or a FWHM of Å for the lines of a neon calibration lamp. The observed spectral range was except for the first run where the range was .
Additional observations were made in August 1989 with the same equipment, but with a lower resolution grating (dispersion of 260 Å/mm). This provided spectra with a resolution of about 8 Å/pixel or a FWHM of Å and a spectral coverage of .
During the night of August 19, 1989 we have also taken spectra in the blue wavelength region with the 130 Å/mm grating. These data cover the wavelength range with a resolution of about 7 Å (FWHM) or 4 Å/pixel. These spectra are useful for the classification of symbiotic systems with G- or K-type giants, namely AG Dra, S190, V741 Per and He2-467.
Schmid & Schild (1994) published a spectropolarimetric survey of symbiotic stars. Their Stokes I spectra are suited for our analysis as well. A detailed description of the observations can be found in their paper.
For the red arm a grating with 158 lines/mm provided a resolution of about 4 Å/pixel or a FWHM of Å for the lines of a HeAr calibration lamp. The wavelength range covered was .
The blue arm of the DBS recorded simultaneously with the near infrared data a spectrum from 3300 Å to 5300 Å with a resolution of about 6 Å (FWHM) using a grating with 300 lines/mm. For our study we selected only the blue spectra of systems with a G or K type giant, where a spectral classification in the near infrared based on TiO bands was impossible. This sample consists of AS201, Wray157, S190, HD 330036, BD-21.3873, and CD-43.14304.
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