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Centro de Astrofísica da Universidade do Porto

Discovery of the `missing' mode in HR1217 by the Whole Earth Telescope

D. W. Kurtz, S. D. Kawaler, R. Riddle, M. D. Reed, M. S. Cunha, M. A. Wood, N. Silvestri, T. K. Watson, N. Dolez, P. Moskalik, S. Zola, E. Pallier, J. A. Guzik, T. S. Metcalfe, A. S. Mukadam, R. E. Nather, D. E. Winget, D. J. Sullivan, T. Sullivan, K. Sekiguchi, X. Jiang, R. R. Shobbrook, B. N. Ashoka, S. Seetha, S. Joshi, D O'Donoghue, G. Handler, M. Müller, J. M. Gonzalez-Perez, J.-E Solheim, F. Johannessen, A. Ulla, S. O. Kepler, A. Kanaan, A. F. M. da Costa, L. Fraga, O. Giovannini, Matthews J. M.

HR1217 is a prototypical rapidly oscillating Ap star that has presented a test to the theory of non-radial stellar pulsation. Prior observations showed a clear pattern of five modes with alternating frequency spacings of 33.3 and 34.6μHz, with a sixth mode at a problematic spacing of 50.0μHz (which equals to the high-frequency side. Asymptotic pulsation theory allowed for a frequency spacing of 34μHz, but Hipparcos observations rule out such a spacing. Theoretical calculations of magnetoacoustic modes in Ap stars by Cunha predicted that there should be a previously undetected mode 34μHz higher than the main group, with a smaller spacing between it and the highest one. In this Letter, we present preliminary results from a multisite photometric campaign on the rapidly oscillating Ap star HR1217 using the `Whole Earth Telescope'. While a complete analysis of the data will appear in a later paper, one outstanding result from this run is the discovery of a newly detected frequency in the pulsation spectrum of this star, at the frequency predicted by Cunha.

Monthly Notices of the Royal Astronomical Society
Volume 330, Page L57
March 2002

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