2. Observations and data reductions
The observations were carried out with the cross-dispersed spectrograph ELODIE (Baranne et al. 1996). This instrument is at the Cassegrain focus of the 1.93 m telescope of the Observatoire de Haute-Provence. The detector was a thinned Tk-CCD, with elements of size 24 µm2.
The observations were obtained during two nights, namely August 1st and 8th, 1994. The spectral domain ranges from 3900 Å to 6800 Å with a resolving power of 42 000. The typical exposure time was 6 min, leading to a signal-to-noise ratio around 50 for the lines considered in this paper (essentially 4553 Si iii and H lines). We reduced the spectra with the INTER-TACOS software (Baranne et al. 1996) that takes care of the offset and flat-field pixel-to-pixel corrections. Finally, the spectra were normalized to the continuum using a cubic spline function and computed in the heliocentric frame.
Approximately, each night represents 1.2 pulsation cycle ( h 50 mn). The pulsation phases were computed using the ephemeris given by Odell (1994): HJD = 2 447 700.1158 + 0.201044444 d.
© European Southern Observatory (ESO) 1998
Online publication: October 21, 1998