A frequency analysis with 20-350 pHz accuracy of five years of observations of the non-linear dipole oscillation in the rapidly oscillating AP star HR 3831

Details A frequency analysis with 20-350 pHz accuracy of five years of observations of the non-linear dipole oscillation in the rapidly oscillating AP star HR 3831 A frequency analysis with 20-350 pHz accuracy of five years of observations of the non-linear dipole oscillation in the rapidly oscillating AP star HR 3831

Dec 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990mnras.247..558k&link_type=abstract

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 247, Dec. 15, 1990, p. 558-572. Council for Scientific

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29

A Stars, Astronomical Photometry, Peculiar Stars, Stellar Oscillations, Accuracy, Harmonics, Stellar Magnetic Fields, Stellar Rotation

Scientific paper

We have carried out 60 hr of high-speed photometric observations of HR 3831 in 1986. The combination of these observations with the 135 hr of observations obtained in 1980/1981 and 43 hr of observations obtained in 1985, for which the total time-span is 1937 d, allows us to analyse the frequencies of the rapid oscillations of HR 3831 without alias ambiguities. We determine seven frequencies (υ1-υ7) with 20-350 pHz accuracy. By examining the relationship between the phase of the, oscillation and the rotation phase, we confirm that the principal oscillation of HR 3831 is mainly due to a long-lived dipole eigenmode whose symmetry axis is the magnetic axis which is oblique to the rotation axis of the star. The basic pattern of the pulsation phase versus rotation phase diagram has remained constant over the five years of observations. An unexplained inequality of the phases, θ(υ2) ≠ θ(υ1,υ1, υ3), indicates that the dipole mode is not purely a normal mode. We confirm that the three first-harmonic frequencies observed in HR 3831 are exactly twice the lowest three frequencies. We show that the high-frequency triplet is not a quadrupole normal mode (l=2) induced by non-linear coupling to the principal dipole mode (l=1); we also show that it is not simply caused by the second-order term of a non-linear dipole mode. The other newly determined frequency (υ7) is separated by the rotation frequency from the second harmonic of the eigenfrequency of dipole mode. We examine the possibility that υ7 may be one component of the second harmonic of the principal dipole mode.

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