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Astron. Astrophys. 348, 831-842 (1999)

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2. Observations

In several seasons (see Table 1), the six CQE stars were observed with the HEROS dual-channel cross-dispersed echelle spectrograph of the Landessternwarte Heidelberg. Via a fiber link, it was used with the ESO 50-cm telescope on La Silla, Chile and with the 1.23-m telescope on Calar Alto, Spain. HEROS covers more than the entire Paschen continuum (3450 Å to 8600 Å) at a resolving power of 20 000. The instrument was described in detail by Kaufer (1998). For the main program stars [FORMULA] Cen, [FORMULA] Cap, and o And, the spectra were taken typically every other week, during a few runs also daily or even more frequently. For comparison, a few spectra were obtained also of well-known proto-typical shell stars.

Further spectra were exposed in November, 1998 during the commissioning period of the newly built FEROS spectrograph at the 1.52m ESO telescope (Kaufer et al. 1997, 1999) and in January, 1999 as part of the guaranteed time observations. The coverage of FEROS ranges from 3700 Å to 8900 Å with a resolving power of 48 000. Since the configuration of the CCD system was not yet fully optimized at the time of these observations, the spectra are affected by relatively numerous bad columns. However, owing to the large number of lines simultaneously observable with FEROS , this does not in any way compromise the significance of the results reported below.

All spectra were reduced according to the procedures described by Stahl et al. (1995) and Kaufer et al. (1997, 1999). Since the CQE's turned out not to be variable on time scales of a few weeks, all spectra of a given observing run (lasting from a few weeks to a couple of months) were averaged in order to increase the signal-to-noise ratio ([FORMULA], in Table 1 given for the range from 4800 Å to 4820 Å).

Additionally, data obtained at La Silla by DB and S with the 1.4-m Coudé Auxiliary Telescope (CAT) and the Coudé Echelle Spectrometer (CES) were used. The data reduction was described by Stefl et al. (1995) in detail.

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© European Southern Observatory (ESO) 1999

Online publication: August 13, 199