2. Observations and data reduction
Using the coudé spectrograph of the NAO 2m telescope at the Rhodope Mountains, Bulgaria, 9 spectra in the blue - spectral resolution of 0.18Å/mm - and 8 spectra in the red - spectral resolution of 0.36Å/mm - photographic region of P Cygni were obtained during 1990. All spectra were converted to relative intensity and wavelength calibrated following the reduction procedure described earlier (Markova 1994). By averaging the spectra in each set we achieved a S/N-ratio of about 45. Since we intend to analize the emission spectrum of P Cygni and since the star is known to exhibit line-profile variations (Markova 1993, Stahl et al. 1994) one may ask whether the use of an average spectrum will be expedient in this case. In fact, the central velocities of the pure emission lines did not show any significant variations during our observing campaign. We also observed small variations of at most 15 km/s in the line widths. Taking into account the quality of the photographic data, the lower intensity of some of the studied lines and the accuracy of the measuring procedure - we use a gaussian fit to the emission lines although they are not always gaussian shaped - we assume, as a first approximation, that the line parameters studied are not time variable, and that we are justified in using averaged spectra.
© European Southern Observatory (ESO) 1997
Online publication: April 8, 1998