A spectroscopic analysis of the beta Cephei star alpha Lupi
P. Mathias
- C. Aerts
- M. De Pauw
- D. Gillet
- C. Waelkens
Received 8 April 1993; accepted 20 September 1993
Abstract:
We present high spectral and time resolution observations of high
signal-to-noise ratio (above 200) of the beta Cephei star alpha Lupi, carried
out for three different wavelengths during three nights. The radial velocity
curves show a nice sinusoidal behaviour for all elements. However, the
amplitude and the average velocity of the variation depend on the considered
lines. By means of a simple least squares fit conducted on each observed night,
we also point out a non-constancy of the pulsation period. A comparison between
the RI and FWHM curves seems to indicate that temperature effects are present
during the pulsation, while the EW varies by about 3
and acceleration curves have a small amplitude, indicating that the motion
does not have any strong non-linear behaviour.
The moment method was used to derive the pulsation parameters. The main mode
was found to be a radial one. Due to the non-constancy of the period and to
the fact that two frequencies were detected in the photometric data, a search
for a second period in the moments has been conducted. Therefore, the moment
method has been generalized for a multiperiodic pulsation. The moments tend
to indicate that a second mode indeed is present. Application of the
generalized moment method to the spectra of alpha Lupi did not lead to a unique
solution for the possible second mode, although the analysisd yields the
presence of a small-amplitude axisymmetric mode with degree 0<l<4.
Keywords:
stars: variable -- lines: profile -- stars: individual: alpha Lupi
-- stars: oscillations
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