Discovery of the `missing' mode in HR1217 by the Whole Earth Telescope
Kepler, S. O.; Kawaler, S. D.; Winget, D. E.; Handler, G.; Ulla, A.; Reed, M. D.; Solheim, J. -E.; Wood, M.; Mueller, M.; Kurtz, D. W.; O'Donoghue, D.; Cunha, M. S.; Metcalfe, T. S.; Matthews, J. M.; Riddle, R. L.; Kanaan, A.; Pallier, E.; Gonzalez Perez, J. M.; Moskalik, P.; Sekiguchi, K.; Guzik, J. A.; Dolez, N.; Fraga, L.; Sullivan, D. J.; Zola, S.; Joshi, S.; Silvestri, N.; Watson, T. K.; Mukadam, A. S.; Nather, R. E.; Sullivan, T.; Jiang, X.; Shobbrook, R.; Ashoka, B. N.; Seetha, S.; Johannessen, F.; da Costa, A.; Giovannini, O.
United States, Portugal, France, Poland, New Zealand, China, Australia, India, South Africa, Norway, Spain, Brazil, Canada
Abstract
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.