Other
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002mnras.337.1059b&link_type=abstract
Monthly Notice of the Royal Astronomical Society, Volume 337, Issue 3, pp. 1059-1067.
Other
23
Stars: Individual: Hr 3831, Stars: Oscillations, Stars: Variables: Other
Scientific paper
We present results of 566 high-dispersion echelle spectra of the roAp star HR 3831. We obtain radial velocities of different ions by cross-correlation with suitable templates. The inhomogeneous abundance distribution results in different rotational velocity curves for different ions. We confirm the large pulsational amplitude in doubly ionized rare-earth ions. In addition we show that, whereas Hα has a large pulsational velocity amplitude, the pulsational velocity amplitudes in Hβ and Hγ are below the detection limit. This supports the idea that the pulsational amplitude is a function of height and that there is a layer enriched with rare earths in the upper atmosphere. We present a list of lines where the pulsational velocity is the largest. In the radial velocities of the NdIII line we are able to resolve the two frequencies of highest amplitude seen in the light variations. Co-added spectra indicate that one of these frequencies is an axisymmetric mode [possibly (l, m) = (2, 0)] and the other a non-axisymmetric mode [possibly (2, -2)]. This confirms recent observations of non-axisymmetric modes in roAp stars. We suggest that the presence of non-axisymmetric modes is simply a consequence of the departure of the eigenfunction from a pure spherical harmonic inclined to the rotational axis and is not related to the Coriolis force. Hence the frequency splitting is precisely equal to the rotational frequency, as observed. Whereas the light variations show strong harmonics, these are not present in the radial velocities.
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