The pulsational behaviour of the rapidly oscillating Ap star HD 122970 during two photometric multisite campaigns |
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| Authors: | GHandler † W WWeiss EPaunzen R RShobbrook RGarrido J AGuzik † AHempel ‡ M BMoalusi T EBeach † RMedupe FChagnon J MMatthews PReegen TGranzer |
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| Institution: | 1South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa; 2Institut für Astronomie, Universität Wien, Türkenschanzstraße 17, A-1180 Wien, Austria; 3Visiting Fellow, Australian National University, Canberra, ACT, Australia; 4Instituto de Astrofisica de Andalucia, Apt. 3044, E-18080 Granada, Spain; 5Los Alamos National Laboratory, X-2, MS B220, Los Alamos, NM 87545-2345, USA; 6Department of Physics, University of Cape Town, Private Bag, Rondebosch 7701, South Africa; 7Department of Physics, University of the North-West, Private Bag X2046, Mmabatho 2735, South Africa; 8University of New Mexico, Los Alamos, 4000 University Drive, Los Alamos, NM 87544, USA; 9Department of Astronomy, University of Cape Town, Rondebosch 7700, South Africa; 10Department of Physics and Astronomy, University of British Columbia, Vancouver, B.C. V6T 1Z4, Canada; 11Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany |
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| Abstract: | We undertook two time-series photometric multisite campaigns for the rapidly oscillating Ap star HD 122970. The first one, conducted in 1998, resulted in 119 h of data and in the detection of three pulsation frequencies. The presence of possible further modes which held the promise of deriving a mode identification motivated a second worldwide campaign in the year 2001. This second campaign resulted in 203 h of measurement, but did not reveal further modes. Rather, one of the previously detected signals disappeared. The two modes common to both data sets have different spherical degree. They also showed slight frequency modulation, and one of them varied in amplitude as well. Possible causes of the latter behaviour include intrinsic instability of the pulsation spectrum or precession of the pulsational axis and orbital motion in a binary system. Frequency analysis of the Hipparcos observations of the star did not allow us to determine the stellar rotation period. The amplitude and phase behaviour of the two modes of HD 122970 in the Strömgren uvby bands is quite similar to that observed for other roAp stars. |
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| Keywords: | techniques: photometric stars: individual: HD 122970 stars: oscillations stars: variables: other |
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