Astronomy and Astrophysics – Astrophysics
Scientific paper
1998-09-23
Astronomy and Astrophysics
Astrophysics
13 pages, 14 figures, accepted by MNRAS
Scientific paper
10.1046/j.1365-8711.1999.02130.x
We present bisector measurements of the H-alpha line of the rapidly oscillating Ap (roAp) star, Alpha-Cir, obtained from dual-site observations with medium-dispersion spectrographs. The velocity amplitude and phase of the principal pulsation mode vary significantly, depending on the height in the H-alpha line, including a phase reversal between the core and the wings of the line. This supports the theory, suggested in Paper I, of a radial pulsational node in the atmosphere of the star. Blending with metal lines partially affects the H-alpha bisector results but probably not enough to explain the phase reversal. We have also detected changes in the equivalent-width of the line during the pulsation, and measured the oscillatory signal as a function of wavelength across the H-alpha region.
Baldry Ivan K.
Bedding Tim R.
Frandsen Soeren
Kjeldsen Hans
Viskum Michael
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