The rapidly oscillating Ap star HD 99563 and its distorted dipole pulsation mode |
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| Authors: | G Handler W W Weiss R R Shobbrook E Paunzen A Hempel S K Anguma P C Kalebwe D Kilkenny P Martinez M B Moalusi R Garrido R Medupe |
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| Institution: | Institut für Astronomie, Universität Wien, Türkenschanzstraße 17, A-1180 Wien, Austria;South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa;Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT, Australia;Observatoire de Genève, Chemin des Maillettes 51, CH-1290 Sauverny, Switzerland;Department of Physics, Mbarara University of Science and Technology, PO Box 1410, Mbarara, Uganda;Physics Department, The University of Zambia, PO Box 32379, Lusaka, Zambia;Department of Physics, University of the North-West, Private Bag X2046, Mmabatho 2735, South Africa;Instituto de Astrofisica de Andalucia, Apt. 3044, E-18080 Granada, Spain |
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| Abstract: | We undertook a time-series photometric multisite campaign for the rapidly oscillating Ap (roAp) star HD 99563 and also acquired mean light observations over four seasons. The pulsations of the star, which show flatter light maxima than minima, can be described with a frequency quintuplet centred on 1557.653 μHz and some first harmonics of it. The amplitude of the pulsation is modulated with the rotation period of the star that we determine with 2.91179 ± 0.00007 d from the analysis of the stellar pulsation spectrum and of the mean light data. We break up the distorted oscillation mode into its pure spherical harmonic components and find it is dominated by the ℓ= 1 pulsation, and also has a notable ℓ= 3 contribution, with weak ℓ= 0 and 2 components. The geometrical configuration of the star allows us to see both pulsation poles for about the same amount of time; HD 99563 is only the fourth roAp star for which both pulsation poles are seen and only the third where the distortion of the pulsation modes has been modelled. We point out that HD 99563 is very similar to the well-studied roAp star HR 3831. Finally, we note that the visual companion of HD 99563 is located in the δ Scuti instability strip and may thus show pulsation. We show that if the companion was physical, the roAp star would be a 2.03-M⊙, object, seen at a rotational inclination of 44°, which then predicts a magnetic obliquity  . |
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| Keywords: | techniques: photometric stars: individual: HD 99563 stars: individual: XY Crt stars: oscillations stars: variables: other |
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