Discovery of the ‘missing’ mode in HR 1217 by the Whole Earth Telescope

• Published in: Monthly notices of the Royal Astronomical Society 2002-03, Vol.330 (3), p.L57-L61
• Main Authors: Kurtz, D. W., Kawaler, S. D., Riddle, R. L., Reed, M. D., Cunha, M. S., Wood, M., Silvestri, N., Watson, T. K., Dolez, N., Moskalik, P., Zola, S., Pallier, E., Guzik, J. A., Metcalfe, T. S., Mukadam, A. S., Nather, R. E., Winget, D. E., Sullivan, D. J., Sullivan, T., Sekiguchi, K., Jiang, X., Shobbrook, R., Ashoka, B. N., Seetha, S., Joshi, S., O'Donoghue, D., Handler, G., Mueller, M., Gonzalez Perez, J. M., Solheim, J.-E., Johannessen, F., Ulla, A., Kepler, S. O., Kanaan, A., da Costa, A., Fraga, L., Giovannini, O., Matthews, J. M.
• Format: Article
• Language: English
• Subjects: stars: individual: HR 1217; stars: magnetic fields; stars: oscillations; stars: variables: other
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1046/j.1365-8711.2002.05294.x

HR 1217 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 34.6 μHz, with a sixth mode at a problematic spacing of 50.0 μHz (which equals 1.5×33.3 μHz) to the high-frequency side. Asymptotic pulsation theory allowed for a frequency spacing of 34 μHz, 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 34 μHz 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 HR 1217 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.