A photometric and spectroscopic study of the hottest pulsating extreme helium star, V2076 Oph (HD 160641) |
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Authors: | D. J. Wright A. E. Lynas-Gray D. Kilkenny P. L. Cottrell R. R. Shobbrook C. Koen F. W. van Wyk P. M. Kilmartin P. Martinez A. C. Gilmore |
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Affiliation: | Mount John University Observatory, Department of Physics &Astronomy, University of Canterbury, Private Bag 4800, Christchurch, New Zealand;Department of Physics, University of Oxford, 1 Keble Road, Oxford OX1 3RH;South African Astronomical Observatory, PO Box 9, Observatory 7935, South Africa;Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT, Australia;Department of Statistics, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa |
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Abstract: | We present results from a three-site photometric and high-resolution spectroscopic campaign on the hottest known extreme helium star V2076 Oph (HD 160641). A core programme of intensive observations covered two weeks and a much lower sampling rate extended over another two months. Despite the fact that the data seem to indicate periodicity near half a day (though the light curves are clearly not formed by a single periodicity), conventional Fourier analysis of the data fails to reveal coherent frequencies. Furthermore, we are unable to recover frequencies which were apparently clear in an earlier campaign on the star. Evidence of monotonic pulsation amplitude changes is seen at the higher frequencies from a wavelet analysis, but more data are needed before this study can be extended to lower frequencies. The application of linear stochastic differential equation (LSDE) methods indicates that the observed light variations could be a result of random variations giving the appearance of intermittent periodicity. High-resolution spectroscopic observations were obtained during the campaign and additional observations were made three years later. Complex line profile variations were observed. It is proposed that the different behaviour of the emission line studied may indicate it is associated with a stellar wind or resident circumstellar material. The frequencies that are extracted from the velocity data do not conform to those identified in the current or previous photometric campaigns. |
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Keywords: | stars: chemically peculiar stars: individual: HD 160641 = V2076 Oph stars: oscillations stars: variables: other |
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